Hey guy's I need some opinions, I think I've isolated my problem finally. I have a 1990 F350 with dual tanks, 460.

Ok, when I bought this truck the pumps would NOT work, fuel gauges read nothing except rear tank. I Narrowed it down to zero power to any of the pumps, I bypassed the stock wiring with a key 12 volt source and went straight to the pump. Walla! Pump on, truck runs.

I've been without gas gauges or rear tank for a while now. Well I'm tired of filling up when I think its low. I pulled the switch out of the dash and had the harness in hand, I had a 12 volt test probe and I touched each of the pins, one turned the rear pump on ( I can hear it going), and front pump works cause I use it everyday. So this points to me as the switch is bad, or no power to it. I already changed the fuel relay which also clicks on every time.

If I have the switch all hooked up and try to switch to rear tank the gauge reads fuel, but pump does not turn on. Switch to front pump, no gauge reading, and in stock form the pump wouldn't turn on, but pump obviously is on because I wired it that way.

What do you all think? I really appreciate it!

thanks, matt

 

I am pulling a code 87 and 95. Fuel circuit failure on both ends.

 

You either have:
open fuse link
bad selector switch
bad Inertia Switch (try to reset it)
bad wiring
bad computer.

You have the bottom relay in the image below:


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I think I know the culprit. Studying that diagram real fast there is a yellow wire that was all taped up at the starter relay, pulled the tape back and it had tons of corrosion in it. I remember seeing that a while ago. Thanks for the reply!

 

corrosion=death

 

ok I've been pickin wires for a while now. I've narrowed it down slightly. Ok I got the fuel gauges to work, some stupid connector was loose.

Now the hard part. I Have Power out of all wires on the fuel relay, except a little black one. I have power at the Inertia switch, No power at the fuel switch for the pumps. Im not sure whats going on here. If I manually Energize the fuel pumps they turn on. So somewhere between the switch to power is broken.

Also the wiring diagram doesnt seem to match my colors. I have no brown at the relay, but I do at switch??

 

It is the blasted switch! I get power at the terminals in the plug, I forgot the two second prime thing. I just left the key on. I tested the pumps with a jumper wire, they both work and the fuel gauges. SWITCH!!! Now I just gotta find one . .

 

Ok guys put the new switch in, what do ya know! My pumps work and the gauges all work. Everything works great!

only one more problem! my front gauge is a bit off . . rear tank reads right, but front when its full only reads about a little over a 1/4. Any insight? Before the switch quit working it worked fine.