If you are using an external voltage regulator to control your alternator as a part of your Megasquirt installation, this page may interest you. Installation of the external voltage regulator will cause the stock ECU to trigger a battery light and ABS light (if so equipped). The stock ECU grounds a wire which runs to the gauge cluster to turn on the battery light. It does this when you turn the key to ON or when the power at the ECU drops 1V below the desired level or when the power at the ECU rises 1V above the desired level. The desired level depends on temperature. When the engine is running and power at the ECU is within 1V of the desired level, the ECU lets the voltage at this wire float (no connection). This wire is solid blue. It is pin 37 on the 1995, but other years will vary. If you have ABS, the solid blue wire splits off to go to the ABS ECU. When the ABS ECU detects that the wire is grounded, it turns on the ABS light and disables the ABS solenoids via a green/red stripe wire. You paid for that ABS, so you probably want it to work, right? And the battery light is a nice feature because it can warn you if your alternator belt shreds. You can kill two birds with one stone (or two lights with one circuit):
This circuit functions similarly to the stock ECU logic. If the voltage is low (12.X volts), it grounds the wire and turns on the battery light. If the voltage is high (13.X volts), it lets the wire float and turns off the battery light. When you turn the key to ON, the battery light turns on. As soon as the engine starts, the battery light turns off. The ABS ECU likes this and turns off the ABS light. Your brakes work as intended and everyone is happy.
Contributed by Corbin
Cars Modifications Power Tuning Megasquirt Battery Light
Last modified on 2011-05-31 21:06:14