85 F150-302 FI. Where do the 2 fuel pumps get their ground?
Schematic shows chassis ground but mine appear to go into wiring harness going towards firewall.Does the EEC supply ground for both pumps?
When I stuck sharp end of probe into brown wire coming from fuel pump relay, probe lit and both pumps kicked on!?!
Any ideas???

 

I believe a lot of the grounds for the rear harness area end up at the driver's side front radiator area.

The EEC supplies a ground to activate the pump relay, not the pump itself. You can ground the correct terminal on the EEC test port plug, and the relay will kick the pump on.

 

They ground under the dash on a support bar just the passenger side and above the heater control box. There are several ground wires that splice together under the dash and run to this point. The only practical way to access it is to remove the dash pad and go in through the top. It's tough to see and even tougher to get a socket on.

 

I ground the EEC test port and both pumps came on.Jumped out the inertia switch but it made no difference.
Got 12V on yellow wire at fuel pump relay and 12V on brown wire with switch on but it's not making it back to the pumps for some reason.Startled me when pumps came on by simply putting probe into brown wire.Doesn't make sense since I didn't actually complete the circuit for the pumps,just the probe.
Felt the fuel pump relay click at the same time but it must have been working already because I don't have power on the brown wire until ignition switch is turned on.
So I'm thinking maybe the pumps just don't have good ground but is my thinking off track?

 

I've had something similar happen in the past...check your EEC grounds. One runs directly to the negative battery terminal. The other runs to one of the wiper motor mounts.

 

Hey,
What does the inertia switch look like? I tried looking for it but I don't know where it is. Is it inside the cab? What is its purpose?

 

What year/model truck do you have? Which engine?

 

86 150 with a 302

 

Your inertia switch is in the cab on the firewall, passenger side, just to the right of heater floor ducts. It looks like a black plastic box with a two wire plug in the bottom and a white push switch on the top right.

 

I checked both grounds mentioned.Even tied them straight to neg. side of battery.Still no power to the pumps unless I ground them at the test port or put a probe light into the brown wire from the fuel pump relay (with ignition switch on).
I just don't understand why the test probe causes the fuel pump relay to click and pumps simutaneously come on simply by sticking the sharp end into the brown wire that already has voltage headed to the inertia switch?
Any electrical gurus out there want to enlighten my dumb a$$?

 

https://www.ford-trucks.com/forums/6...el+pump+relays

Try reading through this thread...