1987 V10 fuel pumps, gas guage not working

[Shoote]

I am out of ideas. 1987 V10 with factory dual tanks. I replaced both tanks and sending units about 2 years ago. All worked fine. Put in a big block with a carb and an inline fuel pressure guage about 1.5 years ago. Everything worked good. Drove the truck last week. Shut it off and it would not restart. Now the gas guage does not work and the fuel pumps are not working on either tank, no pressure on fuel guage. I have replaced the tank selector switch on the dash and the fuel relay switch on the firewall. No change after replacing both items. What am I missing? Thank you for any help you can provide!

Oil pressure guage works when cranking the engine, volt guage works also.

 

[Robert Bare]

Well, you also have a selector valve. Need to check power and grounds. Is possible it is stuck, also, key on, and lightly tap it.

 

[Shoote]

The selector valve.....is that the valve down on the frame rail near the passenger side tank?

 

[Robert Bare]

Don't know where it is on your truck, but, yes, underneath, on frame, bunch of hoses and wires going to it.

 

[Broken85]

Unplug the switch valve under the truck. Get a test light and check for 12v on the tan/ white wire. This is not a dual tank wiring diagram, so I am not sure what color the wire is for the passenger side, but tan/white will probably be the driver side tank.
If you have power upto the switch valve, move towards the back of the truck, your problem is towards the tanks, probably the valve seized or corroded.
If you don’t have 12v at the switch valve, move forward, your problem is that direction.

Then check that you have 12v at the switch in the dash. If you do, check that the tank switch switches power between both poles when you check it with the test light. If your switch is working right, but you don’t have power to the pumps, your problem is probably a broken wire between the switch and the switch valve. I doubt this will be the problem since neither tank has power.

If you don’t have power at the switch, it is probably a relay closer to the throttle body, or a broken wire that direction.

Since both tank pumps quit at the same time, I think it will probably be towards the front of the truck. Check if you have 12v at the solenoid you replaced and work forward or back from there.

Since no one said it yet (and they will). Check your grounds!!!!

 

[Shoote]

Thank you for the suggestions. Now I have a direction to go in.

 

[Shoote]

I did some diagnostic on my truck.
I have no power at the tank switch in the cab. I have power on the orange wire only, 12.45 volts at the relay under the hood. I have one wire with power at the tank selector valve on the frame rail. It is a pink wire.
Not sure where to go from here.
Checked grounds and they are good.