MicroSquirt.com read only forum (Jan.15,2018)

I have just ordered my MS-II (V3 board) unit and am trying to make a wiring diagram for my self so I know what wires to cut. I have a 87' Pontiac Fiero and am planing on cutting out the factory ECU (it does not control my gauges). I was looking at my factory diagrams and the stock ECU gives the fuel pump relay power to turn the pump on.

My question is does MS give the relay Ground or Power to turn the fuel pump on? (in the MS diagrams it looks to be ground)

Can I make it so MS will give either one power or ground?

I want to be able to cut only the wires needed to install MS. I will then go and find a male or female (what ever will plug onto the MS wiring harness) DB37 connector and wire it to the factory ECU pigtail. This way if i have a problem with MS I can simply just unplug the DB37 MS harness and plug in my stock ECU back in. The only problem I see is If they give different signals to the fuel pump relay I will have to make up some kind of switch.

The MS gives ground when on, there will be ways round it to supply 12v when on with a bit of re-wiring.

It`s an odd setup you have, most car ecu`s use a negative trigger for just about everything..

Thanks keithmac for your help.

I think I will just wire a switch in to ground so if I want to put the factory ECU back in all I have to do is flip the switch to turn the fuel pump on.

you could just use the MSII fuel pump output to drive a relay that supplies your original fuel pump relay with power making the original relay operable by either controller. You might want diodes in the power lines to prevent one controller from backfeeding the other.

you could just use the MSII fuel pump output to drive a relay that supplies your original fuel pump relay with power making the original relay operable by either controller. You might want diodes in the power lines to prevent one controller from backfeeding the other.

That's exactly what we did on a golf GTI that needed a +12v to activate the stock fuel pump relay. Two relays in cascade .. kinda weird but it worked great !
-Phil