85 F150 5.0 Fuel Injected. Fuel pump relay has 4 wires coming out of it. Tan with black hash marks/ brown/ red/ yellow/ Does anyone have a wiring diagram non Haynes for the 85 and the PO spliced a ground to the tan wire so the hi pressure fuel pump runs constantly when key is on. All recomendations on where to start appreciated. Also won't display codes.

 

An 1986 should be very close to what you have and I can email you the diagram if you like, just email me your email address. Mine is is below.

But anyway the RED wire comes from the EEC POWER relay and goes to power the coil of the fuel pump relay.
The Yellow wire is pump power from a fuse link hooked to the starter relay and going to the common contact of the fuel pump relay.
The Tan wire with the black hash (or green) comes from the EEC Computer and the Self-Test connector and goes to the other end of the coil of the fuel pump relay to give a ground for the relay to make.
The brown wire hooks to the normally open contact of the fuel pump relay and goes to provide power to the Inertia switch.
The other wire leaving the Inertia switch goes to the high pressure pump and the fuel selector switch (if you have two tanks) on the dash for powering the in-tank pumps.

 

Thanks subford. So what would you guess is the cause of the hi press fuel pump not priming when I remove the homemade ground from the tan/ltgrn (Which goes to the the diagnostic port) thats spliced in? Basicly the previous owner is simulating a grounding at the diag port for continous operation when key is on.

 

There is only about two things it could be.
1. an open in the wiring or plug from the fuel pump relay to the pin on the EEC Computer.
OR
2. A bad EEC computer.

And you said you can not get the EEC Computer to do a self-test so it does not look good for the EEC Computer.

 

By the way make sure the small black wire hooked to the NEG (-) post of the battery and going to the computer has a good ground at the battery post.
Also make sure the computer has a good ground(s) on both ground pins.

 

Thanks for the info. Truck runs well but I just don't like the Fuel pump running nonstop when key is on.