sending unit wiring ?

[jglassjr]

I have a 59 Apache with a gas gauge not working..when I turn on the key the needle goes to full... here is a pic of the top of the tank. the white wire is just tied off. Can someone tell me what I got going on here? To say electrical is not my thing would be an understatement! do I just connect this wire to a good ground and Ill be fine....or?

[OrrieG]

Brown is the factory wire to a post on the gas gauge, it is grounded thru the sender. The white is something someone added, maybe because the brown has a short? At the gauge a pink wire comes from the ignition switch to the other post. As the sender float moves a potentiometer varies the ground ohm rating moving the gauge. The sending unit has a copper strip that eventually breaks. Since you have access, I would pull the sending unit then you can bench test it with a jumper wire to the gauge to see if it work (sender body will need to be grounded).

[Stepside Jim]

On my 57, there needs to be a ground wire attached to one of the sending unit screws then directly to ground.

I think one of those wires is to be a ground wire.

Jim

[Old Crow]

Jim's probably right about the extra wire being a ground.
Normal operation for the gauge is to peg over full if the circuit to the sender is open. If it's shorted to ground the gauge pegs on the empty end of the scale(this is also a quick and dirty test to check the gauge and the wire to the sender).

[OrrieG]

Thinking about it ground wire is probably needed because the tank does not bolt directly to the cab and interference fit between straps and tank could compromised over time. Other ground circuit would be thru the fuel line to fuel pump and block. I do not remember mine having a second wire.

[Old Crow]

Orrie, stock fuel lines had rubber hose at the tank and at the pump. This renders the fuel line useless as a ground.
Most of the vehicles we put together have had the tanks, the straps(if any)and the frame painted. No good path for ground. We run a separate ground to the tank on everything we build for this reason.

[mr48chev]

I'd say that "pink" light colored wire was someone's ground wire a one time. easy to figure out, were does the other end connect. Otherwise it may have been a bypass wire for the original wire due to a defect in the original wire then someone hooked up the original wire while working on the sender. In other words TRACE THE WIRES and see where they go.

[OrrieG]

Old crow, yesterday was brain fart time for me, should have thought it through before posting. I just don't remember second wire but it was probably there. My new back tank gauge works fine with one wire, but the tank is bolted directly to the frame.

[jglassjr]

thx guys for chiming in and offering help... Ill ground the light colored wire and see what happens... Im away from my baby for 3 weeks so Ill have to wait for abit

[mr48chev]

I think I would just make up a new ground wire with an eye on each end and put one eye under one of the screws holding the sending unit down and ground the other end to the sheetmetal of the cab with a short sheet metal screw. Not though the back wall of the cab though.

[Old Crow]

Originally Posted by OrrieG

Old crow, yesterday was brain fart time for me, should have thought it through before posting. I just don't remember second wire but it was probably there. My new back tank gauge works fine with one wire, but the tank is bolted directly to the frame.

Yeah, we use those conversion tanks on most of the trucks we build. I still like to run a ground wire because both the tank and frame are usually painted, and I don't always trust that connection.
Call me anal(my wife does all the time).