gas gauge

I'm need help with fuel gauge issue it works on drivers side tank and not the other
the previous owner replaced tank and sender it reads right on full not passed full
on the one not working . my question is does that sending unit get power from the tank selector
valve so when I switch to passenger tank there should be 12 volts to sender?

cape square body said:

I'm need help with fuel gauge issue it works on drivers side tank and not the other
the previous owner replaced tank and sender it reads right on full not passed full
on the one not working . my question is does that sending unit get power from the tank selector
valve so when I switch to passenger tank there should be 12 volts to sender?

Click to expand...

it takes a ground. the sender needs to be grounded to the truck frame, and the wire from the sender that goes to the switch yes

I would say if you never had the tank down maybe its time to bring down and then play with the arm, the thing may just be froze

As AuroraGirl said, make sure the sending units are grounded. Unscrew the bolt, sand down the frame to bright metal, and screw back in. Also follow the wire up and make sure it’s still connected to the sending unit.

An 87 uses a solenoid with 6 terminals, so you will have to determine which one is which, and where 12 volts is applied. I think that newer solenoids also stay in each position (left or right) even when you turn off the ignition.

The old single-terminal solenoids were simpler because they defaulted (with no power) to the main tank, and when 12 volts was applied they switched to the aux tank.

the sending unit is a resistance which contains two cables, one is grounded and the other goes to the gauge so the resistance changes per the gas level, of course both thanks are the same. Then the fuel tank selector valve switches who's tank is sending the resistance to the gauge. In the image you can see that the Pin A is where the passenger side sending unit is connected while pin C is where the driver side sending unit is connected, pin B is the signal that is sent to the gauge. Not sure how easy is for you to get a 100 ohms potentiometer (three pins), if so, first disconnect the harness from the fuel tank selector valve, you can connect ground to the middle of the pot and one of the remaining pins to the fuel tank selector valve harness you previously disconnected (C305 in the image) to pin B, turn on the key and move the pot value, the gauge should move, then you confirm that the sending unit needs to be replaced or maybe is not well grounded.

Sorry, attaching the image

AuroraGirl is so smart... LOL.