Click on our menu buttons immediately below to find MegaSquirt® information quickly:


MicroSquirt® Wiring

General Automotive Wiring Guidelines

There are a number of tools and techniques you will need to wire MicroSquirt® to your vehicle. You will also need some specialized knowledge. We will try to present an overview of everything you need here (if you have questions, ask them on the forums at www.microsquirt.com):

Tools:

Supplies:

Of course you will also need a PC computer to run the tuning software. Any computer that can run Windows 98 or higher (i.e., WinMe, WinXP, WinVista) will work. Ideally the computer will have a serial port (9-pin male connector), but many USB/Serial adapters have been used successfully. A laptop computer is easiest to use in the vehicle, of course, and cheap older laptops with Win98+ and a serial port are commonly available at low cost.

Wiring Procedure

NOTE: The wire labeled "Vref" is the +5V voltage source for the MAP sensor and the TPS sensor. This wire only connects to these components (and possibly the LEDs, if used), so be very careful to not connect this directly to ground or (worse) +12V battery. Bad things will occur if you mis-wire this one - double check your work.

When wiring up a vehicle, we recommend performing this in discrete and deliberate stages - this is how to approach this:

  1. You may wish to use the MicroSquirt® access board, which can simplify the wiring for many installations.

  2. Always make sure the dangling wires on the MicroSquirt® harness are not touching each other or any metal (ground return path). Next, wire up all of the sensors (TPS, EGO, coolant, intake air temp, MAP) and the signal return grounds (use the sensor ground return wire for these). Then hook up the main ground wires to the engine block and the switched +12V for the +12V lead. Check again to make sure the remaining dangling wires (which includes the outputs - you have not hooked them up yet) are insulated from each other and anything else - tape these if need be.

  3. Hook up the laptop and run MegaTune and establish communications - remember that with the latest MS-II embedded code (V2.881 and later) you need to set the "ECU Type" to MicroSquirt® the first time you run (click the "burn to ECU" button for this and any other change to stick). Until you set the ECU Type, all the other parameters will be grayed out.

  4. Let MegaTune and the MicroSquirt® just run for a while and talk to each other, at least for several minutes. If there are any communications burps/hiccups, this is the time to find them out and correct (it's a nice, clean electrical environment at this point). Do not worry about the MicroSquirt® sucking down the vehicle battery, its current draw is around 40 milliamps, so it is a very small load - the dome light above your head draws many times more current. This is also a good time to get familiar with MegaTune - set up the number of cylinders, REQ_FUEL, ignition trigger type, etc. - and, maybe save off a MSQ or two, just to get the feel for how it all works. Read Configuring MegaSquirt-II for information on configuring MicroSquirt® and MegaTune. You should also: If this works as expected (the sensor values look good, the TPS values aren't backwards, you have set the correct MAP sensor type, etc.), you are in great shape, and you are potentially minutes away from a running engine.

  5. Also, in this state, with no ignition or injectors hooked up (and no fuel pump active), turn over the starter motor with the MicroSquirt® turned on and MegaTune running. This is a big current draw and if there are grounding issues you will see the sensor readings jump all over the place - if so then check your engine-to-battery-to-chassis grounds (see the sticky on this). Less of an influence but perhaps more fun is to turn on the windshield wipers, heater fan, headlights, and even blow the horn - each of these can produce noise on the +12V feed and it is better to find this out now so you can rectify instead of tracking down, say, a random tach glitch that is really caused by battery feed noise - it happens.

  6. Next, hook up the tach input source, and check for tach signal with MegaTune with the starter cranking. If you are using EDIS, GM DIS, or HEI module it is often better to test this along with the outputs (next step).

  7. Finally, hook up the fuel pump relay, injectors, and ignition. And then start it up (they always start right up, or at least do something), tweak the tune, and drive away! Read Tuning MegaSquirt-II for information on tuning.

For each circuit, you will need to:

  1. Choose the order of circuits you will work on. Generally, this should be:
    1. Power and ground circuits. Completing this step will let you power up MicroSquirt® EFI controller, and test the connection to MegaTune on your tuning laptop.
    2. Sensors:
      • Coolant and Intake Air Temperature sensors (CLT and IAT),
      • Throttle Position Sensor (TPS),
      • Exhaust Gas Oxygen (EGO, aka O2) sensor (if used),
      • Manifold Absolute Pressure (MAP) sensor.
    3. Actuator and Injector Outputs: These include:
      • Fuel Pump,
      • Fast Idle (if used),
      • Ignition control module (if used),
      • Injectors.
    4. Ignition Inputs and Outputs:
      • Ignition Inputs ("tach" signal(s)),
      • Ignition Outputs (coils or ignition module driver(s))
    (Many of these are broken out separately from the main wiring diagram below to make it easier to follow.)
  2. For each item in your list, identify the wires you need to connect from the list and wiring diagram below and your vehicle wiring diagram.
  3. For each wire, crimp or solder the connection:
  4. Slide the heat shrink tubing over the connection, center it over the connection, then shrink it into place with a heat source.
  5. Verify that you have made the correct connection(s) at each step.
  6. After each step, test the function of the unit. For example, you can see if:

Wiring MicroSquirt® to the external harness is much the same as with MegaSquirt-II, and you can read much more about that here: www.megamanual.com/v22manual/mwire.htm. You use the same sensors, etc.

However, because of the change to the AMPSEAL connector (from the DB37), and the absence of the DB9 connector, the external connections are somewhat different. The AMPSEAL connections are:

To wire MicroSquirt® EFI controller, you need to make the following connections:

PinNameFunctionHarness Wire Color(s)
(main/stripe)
Pin112 Volt SupplyThis connects to a switched 12 Volt supply. Use the ignition switch to control a relay that provides 12 volts to both the MicroSquirt® and the injectors.Red
Pin2CAN HighThis is one of two Controller Area Network (CAN) communications lines, used to communicate with MegaSquirt peripherals.Blue/Yellow
Pin3CAN LowThis is one of two Controller Area Network (CAN) communications lines, used to communicate with MegaSquirt peripherals.Blue/Red
Pin4VRIN2+Second ignition input signal (Input 2) for a cam position sensor or second crank sensor with the Dual Spark option.Brown/White
Pin5Spare InputThis is a second spare ADC(ADC7). It is used for alternate MAF pin or knock sensing, but it can be used to record whatever 0-5 Volt signal is put on it if neither the MAF option nor the knock option uses it. In this case it is stored in outpc.knock.n/a
Pin6Flex FuelFor input from a ethanol Flex Fuel sensor.Purple/White
Pin7FIDLEThis is the output for controlling an ON/OFF style FIdle or a PWM style IAC (usually found on Fords). You cannot use a stepper type IAC (with 4 pins), only FIdle (on/off) or PWM style idle valves (2 pins) are supported.Green
Pin8FUEL PUMPThis output controls a fuel pump relay by providing a ground when the fuel pump should be running. It cannot control a fuel pump directly.Purple
Pin9INJECTOR 1This pin connects to the injectors. You connect half the injectors on one bank (INJECTOR 1) and half on the other (INJECTOR 2). These connect to one pin on each connector. The other pin on each connector is supplied with 12 Volts through the main relay (see diagram) and the INJECTOR pins ground the injectors to 'fire' them and squirt fuel.Green
Pin10INJECTOR 2This pin connects to the injectors. You connect half the injectors on one bank (INJECTOR 1) and half on the other (INJECTOR 2). These connect to one pin on each connector. The other pin on each connector is supplied with 12 Volts through the main relay (see diagram) and the INJECTOR pins ground the injectors to 'fire' them and squirt fuel.Blue
Pin11IGNITION OUTPUT #2Second ignition output signal. Note that this wire can be used to directly control one coil, and it can carry up to 7.5 Amps of current (be sure to read MicroSquirt® Direct Coil Control).

The coil's primary current can generate a lot of noise inside the MicroSquirt. The whole MicroSquirt® setup is very compact and noise coupling in the wires can be of concern. Running this wire (and the IGNITION OUTPUT #1 where appropriate) in their own shielded "conduit", along with the injector outputs, can substantially reduce noise injection back into the tach circuit. You can buy shielded wire for this, or wrap 2 to 3 layers of aluminum foil (have a look into your kitchen) around the wires and connect the shield to ground.

White/Red
Pin12IGNITION OUTPUT #1Ignition output signal. Note that this wire can be used to directly control one coil, and it can carry up to 7.5 Amps of current (be sure to read MicroSquirt® Direct Coil Control).

The coil's primary current can generate a lot of noise inside the MicroSquirt. The whole MicroSquirt® setup is very compact and noise coupling in the wires can be of concern. Running this wire (and the IGNITION OUTPUT #2 where appropriate) in their own shielded "conduit", along with the injector outputs, can substantially reduce noise injection back into the tach circuit. You can buy shielded wire for this, or wrap 2 to 3 layers of aluminum foil (have a look into your kitchen) around the wires and connect the shield to ground.

White
Pin13SERIAL RxThis pin is used to receive data from the laptop computer serial port (usually a DB9 or DB25). It is connected to Pin3 on a DB9 connector (Pin2 on a DB25) to plug into your laptop/notebook computer.Red (pre-wired to jack)
Pin14SERIAL TxThis pin is used to receive data from the laptop computer serial port (usually a DB9 or DB25). It is connected to Pin2 on a DB9 connector (Pin3 on a DB25) to plug into your laptop/notebook computer.Orange (pre-wired to jack)
Pin15BOOTLOADERThis pin is grounded to enter bootloader mode, which allows you to update the embedded code in MicroSquirt. You can connect this lead to a switch, with the other side of the switch connected to ground. When you close the switch and reboot MicroSquirt® EFI controller, you will be in bootloader mode.Purple/Black
Pin16ACCEL LEDThis is the supply for an 'acceleration indicator LED'. You connect the cathode (short lead) of and LED (light emitting diode) to this wire. The longer lead of the LED you connect to a 330 Ohm resistor, then connect the other side of the resistor to the Vref wire (5 Volts). Be certain that Vref will not be grounded or connected to 12 Volts. Or you could use some other voltage source beside Vref. For example, you could use the battery supply voltage (nominally 12 Volts) as long as you increase the current limiting resistor value to 1K Ohms (to keep the current within limits). The LED will then light whenever accel enrichment is in effect.

When used as a spare port, this output can drive up to 5 Amps absolute maximum (4 Amps is a safer limit)

Yellow/Black
Pin17WARM-UP LEDThis is the supply for an 'warm-up indicator LED'. You connect the cathode (short lead) of and LED (light emitting diode) to this wire. The longer lead of the LED you connect to a 330 Ohm resistor, then connect the other side of the resistor to the Vref wire (5 Volts). Be certain that Vref will not be grounded or connected to 12 Volts. Or you could use some other voltage source beside Vref. For example, you could use the battery supply voltage (nominally 12 Volts) as long as you increase the current limiting resistor value to 1K Ohms (to keep the current within limits). The LED will then light whenever warm-up enrichment is in effect.

When used as a spare port, this output can drive up to 5 Amps absolute maximum (4 Amps is a safer limit)

Yellow/White
Pin18N/C (ground)Not Usedn/a
Pin19SERIAL GROUNDSerial communications dedicated ground.Green (pre-wired to jack)
Pin20SENSOR GROUNDThis is a dedicated sensor ground wire. All of the sensor grounds can be connected to this wire to reduce then possibility of electrical noise.White/Black
Pin21GROUNDThis is one of several ground wire pins (18 through 23). All of the ground wires should be run to the same spot on the engine (to avoid ground loops). Make sure you have a good ground connection from the batteries negative terminal to the engine, and from the engine to the frame as well.Black
Pin22GROUNDThis is one of several ground wire pins (18 through 23). All of the ground wires should be run to the same spot on the engine (to avoid ground loops). Make sure you have a good ground connection from the batteries negative terminal to the engine, and from the engine to the frame as well.Black
Pin23GROUNDThis is one of several ground wire pins (18 through 23). All of the ground wires should be run to the same spot on the engine (to avoid ground loops). Make sure you have a good ground connection from the batteries negative terminal to the engine, and from the engine to the frame as well.Black
Pin24MAPThis pin is connected to the output from a MAP sensor that puts out a 0 to 5 Volt signal (roughly) proportional to absolute pressure. General Motors MAP sensors are suitable (Pin24 connects to pin B on the sensor, pin A is grounded, pin C gets 5 Volts from Vref (Pin28 on MicroSquirt)). You can also use the original MPX4250 MAP sensor used with MegaSquirt, you connect the pion #24 to the sensor's Pin1, Pin2 is grounded, and 5 Volts (Vref) is connected to pin#3.Green/Red
Pin25CLTMicroSquirt® uses the coolant temperature to determine the warm-up enrichments. The sensor must be a negative temperature coefficient (meaning the resistance decreases as the temperature increases). Most automotive temperature sensor are this type, however the default sensors are General Motors sensors.Yellow
Pin26IATMicroSquirt® uses the intake air temperature (aka. manifold air temperature = MAT) to determine the air density for fuel calculations. The sensor must be a negative temperature coefficient (meaning the resistance decreases as the temperature increases). Most automotive temperature sensor are this type, however the default sensors are General Motors sensors.Orange
Pin27TPSThis is a pin for the 'sense' connection on a throttle position sensor.

To hook up your throttle position sensor (TPS), disconnect the TPS, and use a digital multi-meter. Switch it to measure resistance. The resistance between two of the connections will stay the same when the throttle is moved. Find those two - one will be the +5 Vref and the other a ground. The third is the sense wire to MegaSquirt. To figure out which wire is the +5 Vref and which is the ground, connect your meter to one of those two connections and the other to the TPS sense connection.

If you read a high resistance which gets lower as you open the throttle, then disconnected wire is the one which goes to ground, the other one which had the continuous resistance goes to the +5 Vref from the MegaSquirt, and the remaining wire is the TPS sense wire.

Blue
Pin28VrefThis is a 5 volt supply for the throttle position sensor and the MAP sensor. DO NOT connect it to 12 Volts! The wire labeled "Vref" is the +5V voltage reference for the MAP sensor and the TPS sensor. This wire only connects to these components, so be very careful to not connect this directly to ground or (worse) +12V battery. Bad things will occur if you miswire this one - double check your work.

If your MicroSquirt has processor resets once installed, hooking up an external capacitor to Vref helps. Anything from 47µFarads up to 1000µF on the Vref to sensor ground return will help.

Gray
Pin29SPARE ADCCan be used for external baro MAP sensor.Orange/Green
Pin30OPTOIN+Square wave ignition signal input positive connection for Input 1. Note that you can use only one of OPTIN+/- or VRIN+/-, because they connect to the same processor pin. For the second ignition input (Input 2), use VR2IN+ (Ampseal pin 4).

If you are triggering directly off the coil (instead of something like a missing tooth wheel or another relatively low-voltage signal), connect OPTOIN+ (Ampseal pin #30) to the coil's negative terminal as usual, but connect the OPTOIN- (Ampseal pin #31) to a 12V source rather than grounding it. This then uses the flyback spike off the coil as a trigger (rather than the 12 Volt signal). Doing this reduces the energy dissipated in the circuit, prevent a thermal 'melt-down' of the components inside MicroSquirt®.

Gray/Red
Pin31OPTOIN-Square wave ignition signal input negative for Input 1. Note that you can use only one of OPTIN+/- or VRIN+/-, because they connect to the same processor pin. For the second ignition input (Input 2), use VR2IN+ (Ampseal pin 4).

If you are triggering directly off the coil (instead of something like a missing tooth wheel or another relatively low-voltage signal), connect OPTOIN+ (Ampseal pin #30) to the coil's negative terminal as usual, but connect the OPTOIN- (Ampseal pin #31) to a 12V source rather than grounding it. This then uses the flyback spike off the coil as a trigger (rather than the 12 Volt signal). Doing this reduces the energy dissipated in the circuit, prevent a thermal 'melt-down' of the components inside MicroSquirt®.

Gray/Black
Pin32VRIN1+Variable reluctor A/C signal input for Input 1. Note that you can use only one of OPTIN+/- or VRIN+/-, because they connect to the same processor pin. For the second ignition input (Input 2), use VR2IN+ (Ampseal pin 4)Silver (coax center wire)
Pin33VRIN-Variable reluctor A/C signal input (ground) for Input 1 & Input 2 (if used). Note that you can use only one of OPTIN+/- or VRIN+/-, because they connect to the same processor pin. For the second igntion input (Input 2), use VR2IN+ (Ampseal pin 4)Silver (coax shield)
Pin34O2This is connected to the oxygen sensor output wire. This may be a 0 to 1 Volt signal directly from a narrow band sensor, or a 0 to 5 Volt signal from a wide band sensor controller.Pink
Pin35TACH OUTPUTThis connection can be used to drive a standard tach (OEM or aftermarket). For details on how to hook it to your tach, see your tach installation manual or OEM service manual.Green/Yellow

AMPseal 35 pin Connector

The AMPseal connector has 35 pins, numbered in rows from 1-2, 13-23, and 24 to 35. They are numbers from left to right as viewed looking in to the connector on MicroSquirt. These numbers are also imprinted in the connector itself, if you look carefully.

Injector and Power Wiring

Note that MicroSquirt® and the injectors MUST be powered off the same relay (the 'main relay'). If the injectors are powered while MicroSquirt® controller is not, the injectors might be grounded and flood the engine with fuel.

Grounds

Make sure the grounds are correct. When running the grounds on MicroSquirt® EFI controller, it is important to remember that there are different "types" of grounds. These are:

  1. High power grounds (Ampseal pin 21,22,23) - these are the returns for the fuel injector and ignition drivers, and the fuel pump/fast idle/spare output drivers. There are three wires on the connectors for these, going to pins 21, 22, and 23 on the AMPSEAL - these are for the high power ground path. All three (3) of these wires need to ground direct to the engine block. It is important to run all three wires because it will reduce both the resistance and the overall inductance of the ground return path. Each wire has a resistance, and using three of them in parallel reduces the overall resistance. Equally important, each wire has an inductance, and inductances do not "like" fast-changing signals (like a pulse from a spark) and can cause very brief voltage offsets in the ground path. By having multiple wires it is the same as having multiple inductors in parallel, resulting in an overall lower inductance. At the point on the engine block where the grounds hook together, it is a good idea to run a separate wire from this junction back to the battery as well. This is redundant, however it often cleans up noise from sources like the starter motor. And, if it does help then you should take another look at your big positive and negative wire on the battery. Since we are talking battery - the point where you pick up the +12V to power the MicroSquirt® controller is very important. This will go through a relay in order to turn on and off the MicroSquirt® EFI controller, and the power source for the +12V on the relay needs to go back to the battery, or a path that leads direct to the battery without a long run of wiring. Just like for the grounds, run a separate wire from the relay direct back to the battery just to be sure.
  2. Sensor ground (Ampseal pin 20) - the coolant sensor, intake air temperature sensor, throttle position sensor, and external MAP sensor needs to be grounded back to pin 20 on the AMPSEAL. This is the low-current sensor return path and it needs to be kept away from the high power ground. This wire hooks directly to the sensors only and not to the engine block - it is its own return path.
  3. VR return ground (Ampseal pin 33) - there is a separate VR(-) input on the AMPSEAL, this needs to be connected to the VR sensor(s). If you are using two VR sensors, return both back to this wire (these are low current and can be shared on the one wire return path) Do not ground the VR sensor anywhere else, return the ground back to the VR(-) terminal. On the MicroSquirt® EFI controller, this return goes directly back to the VR input circuit's transistor/op amp and not to the ground plane, this keeps the high amplitude VR voltages (and resulting currents) isolated to the VR circuit.
  4. Serial return (Ampseal pin 19) - the serial cable on the MicroSquirt® has a separate ground return path thru the AMPSEAL connector. This return goes direct to the RS-232 transceiver (and not thru the ground plane, keeping the noise off...).

With the small size of MicroSquirt® EFI controller, keeping the grounds straight is important. It is not hard, just keep things in logical groups - high power stuff goes to engine block, sensors on their own ground loop, and the VR sensor is also separate. The ignition coil current path is from the battery to the ignition coil to the MicroSquirt® driver and back. The same goes on for the injector and general purpose outputs. Lots of juice flowing on this path, it needs to stay away from the sensors. It also needs a low resistance/inductance loop. The Vref is the reference voltage generated by MicroSquirt® EFI controller, it passes thru the sensors and the return ground path comes back to the MicroSquirt. Only one return path is required for the sensors because it is comparatively low current, and we all know that voltage drop across a wire is driven by Ohm's law (V=I*R).

Ignition Wiring

In general, MicroSquirt® can be wired the same as MegaSquirt-II for ignition input (tach) signals. However, there are a few of things to note for those installs that are direct-driving ignition coils with MicroSquirt® (i.e. not using an ignition driver module but the internal VB921 drivers in the MicroSquirt):

If you are triggering directly off the coil (instead of something like a missing tooth wheel or another relatively low-voltage signal), connect OPTOIN+ (Ampseal pin #30) to the coil's negative terminal as usual, but connect the OPTOIN- (Ampseal pin #31) to a 12V source rather than grounding it. This then uses the flyback spike off the coil as a trigger (rather than the 12 Volt signal). Doing this reduces the energy dissipated in the circuit, prevent a thermal 'melt-down' of the components inside MicroSquirt®.

Manifold Absolute Pressure (MAP) Sensor Wiring

This sensor is critical to how MicroSquirt® functions. the MAP sensor tells MicroSquirt® the intake vacuum (or boost) the engine has, and use this to scale the fuel injected. These generally have three electrical connections: 5 Volts, ground, and a signal. In addition to the electrical connections, the MAP sensor also has a vacuum connection the intake manifold - this must be downstream of the throttle(s), in the plenum area.

A separate baro sensor (for full-time barometric pressure sensing, rather than just using the startup value) is connected the same way, but the signal wire is connected to AMP pin 29 via the orange wire with the green stripe. Vref and ground can be shared.

For the popular GM MAP sensors (which come in 1, 2 and 3 bar versions) the wiring is:

and has:

  • Ground on Pin A,
  • Sensor output on Pin B, and
  • +5 Vref on Pin C.
  • (Note that ABC are swapped from the previous diagram!)

    Coolant Temperature Sensor Wiring

    The temperature sensors that are default sensors for MicroSquirt® controllers are General Motors two-pin sensors. A lot of temperature sensors (aka. "senders") designed for gauge use have one end grounded to the threads for contact in the engine block. This is fine for gauge work, but for EFI you will notice that the majority of the sensors have two terminals (and insulated from the case/thread) such that a separate ground to the ECU can be implemented. This to eliminate the possibility of an erroneous ground path introducing errors in the readings.

    One of the pins is ground, and the other goes to MicroSquirt. It doesn't matter which pin you use for which function. You can use other temperature sensors by inputting appropriate values into MegaTune (see: www.megamanual.com/megatune.htm#oh). If you have substituted a one pin connector, the body of the sensor is grounded to the engine, and the pin is connected to MicroSquirt.

    Intake Air Temperature Sensor Wiring

    The temperature sensors that are default sensors for MicroSquirt® controllers are General Motors two-pin sensors. One of the pins is ground, and the other goes to MicroSquirt. It doesn't matter which pin you use for which function. You can use other temperature sensors by inputting appropriate values into MegaTune (see: www.megamanual.com/megatune.htm#oh). If you have substituted a one pin connector, the body of the sensor is grounded to the engine, and the pin is connected to MicroSquirt.

    The IAT sensor must be placed to measure the temperature of the air entering the manifold. In a normally aspirated engine, this can be almost anywhere in the intake tract (air cleaner, throttle body, etc.) since air temperature does not change a lot. For a boosted application (blower of turbocharger), the intake air temperature should be measured in a boosted part of the tract (since compressing the air raises its temperature), and you should use an 'open element' IAT sensor: www.megamanual.com/v22manual/mwire.htm#clt

    Fuel Pump Wiring

    MegaSquirt controls the fuel pump operation. This is to shut the fuel pump down if the engine stalls, preventing the pump from running unnecessarily (or in the case of a crash).

    Exhaust Gas Oxygen Sensor Wiring

    An exhaust gas oxygen sensor (EGO) is optional but useful for tuning with MegaSquirt. You can use either a narrow-band sensor, or the more useful wide-band sensor (with a controller).

    Fast Idle Valve Wiring

    The fast idle valve is used to increase engine speed when the engine is cold, preventing it from stalling. MicroSquirt® can use either a 'solenoid'-style ON/OFF valve, and a variable pulse width modulation valve. See: www.megamanual.com/ms2/IAC.htm#fidle

    Throttle Position Sensor Wiring

    To hook up your throttle position sensor (TPS), disconnect the TPS, and use a digital multi-meter. Switch it to measure resistance. The resistance between two of the connections will stay the same when the throttle is moved. Find those two - one will be the +5 Vref and the other a ground. The third is the sense wire to MegaSquirt. To figure out which wire is the +5 Vref and which is the ground, connect your meter to one of those two connections and the other to the TPS sense connection.

    If you read a high resistance which gets lower as you open the throttle, then disconnected wire is the one which goes to ground, the other one which had the continuous resistance goes to the +5 Vref from the MegaSquirt, and the remaining wire is the TPS sense wire.

    Accel and Warm-Up LED Wiring

    These circuits ground the LED to light them. You can use the Vref 5 volt supply on Pin 28 to power the LEDs, or you could use some other source. For example, you could use the battery supply voltage (nominally 12 Volts) as long as you increase the current limiting resistor value to 1K Ohms (to keep the current within limits).

    Using the Relay Board with MicroSquirt

    Check the MicroSquirt® access board, which may be a better choice than the relay board for some installations.

    You can use MicroSquirt® with a relay board, if you like. You will need to solder many of the leads from the suppled harness (extending them as necessary) to a female DB37 solder cup connector (like Digi-Key 2237F-ND, and a suitable hood (937GME-ND), if desired and if temperatures permit). The connecting cable should be wired like this:

    The above diagram has an error. Pin 32 should be the VR + lead, pin 33 should be the ground. these are reversed in the above diagram.

    Note:



    MegaSquirt® and MicroSquirt® controllers are experimental devices intended for educational purposes.
    MegaSquirt® and MicroSquirt® controllers are not for sale or use on pollution controlled vehicles. Check the laws that apply in your locality to determine if using a MegaSquirt® or MicroSquirt® controller is legal for your application.
    ©2005, 2012 Bruce Bowling and Al Grippo. All rights reserved. MegaSquirt® and MicroSquirt® are registered trademarks. This document is solely for the support of MegaSquirt® boards from Bowling and Grippo.