1973-1991 Dual fuel tank systems theory of operation

[Ford Assassin]

Originally Posted by hatzie

Terminal D, the hot coil terminal of the fuel pump relay, was driven by the TBI ECM on Connector A Terminal 1... if the wiring diagrams are correct. I posted a snippet of the fuel pump circuit in the tech writeup.

The most elegant way to do this would be to drive the relay coil exactly like the original setup.

I'd find the original TBI ECM end of the fuel pump relay drive wire and attach it to the fuel pump drive on the LS PCM. This will offload any high current draws that might make the PCM fuel pump driver transistor unhappy.

You should be able to buzz the original ECM Connector A Terminal 1 wire to the fuel pump relay terminal D to be sure you have the correct wire.

I guess some of the info here is over this redneck's head. Lol

Dumb it down for me, which color wire do I need to splice into on the firewall relay harness to the LS fuel pump wire into to make it all work? The LS harness already has its own 40 amp relay with power just for the fuel pump. It's a single 12v power wire intended to wire directly to a single fuel pump.

Thanks.