Sending unit and gas guage wiring

[62stepside longbox]

Hi everyone, the other day I tried to hook my sending unit up to my gauge. I tested it so I know the sending unit is good. First I grounded it then I hooked the brown wire that comes from the gauge to the to sending unit. Then I turned the key so it would get power and "zap" a small cloud of smoke came from the sending unit and fried it. It no longer works now. So now I got another sending unit and tested it and it works. Any ideas on what went wrong? I don't want to fry this one. Thanks

[62stepside longbox]

Anyone know?

[jtrichard]

Missed wired ? throwing voltage to the sending unit

[Ronw435]

Isn't the sending unit in the gas tank?

[62stepside longbox]

Originally Posted by Ronw435

Isn't the sending unit in the gas tank?

Well it's supposed to be but when I was testing it I had it out of the tank

[jayoldschool]

I'll guess that 12v doesn't go to it, it just gets grounded and has variable resistance to ground.

[Tazimafied]

Originally Posted by jayoldschool

I'll guess that 12v doesn't go to it, it just gets grounded and has variable resistance to ground.

You are correct!


Not sure what is happening in your specific situation Stepside. It sounds like full power went through the brown wire and hit the windings of the sending unit and smoked them. Double check your gauge wiring and test the wire with a volt meter before connecting the new sending unit.

[62stepside longbox]

Originally Posted by Tazimafied

You are correct!


Not sure what is happening in your specific situation Stepside. It sounds like full power went through the brown wire and hit the windings of the sending unit and smoked them. Double check your gauge wiring and test the wire with a volt meter before connecting the new sending unit.

Thanks, I'll test tomorrow to see how much power it's getting. Any idea how much power it's supposed to get?

[Tazimafied]

There shouldn't be any power coming through the brown wire or going to it.

It is basically a ground wire with a rheostat(the windings inside the sending unit) that varies the ohms to ground.

Essentially your gas gauge is a ohm meter that uses a 12 volt power source.

[62stepside longbox]

Originally Posted by Tazimafied

There shouldn't be any power coming through the brown wire or going to it.

It is basically a ground wire with a rheostat(the windings inside the sending unit) that varies the ohms to ground.

Essentially your gas gauge is a ohm meter that uses a 12 volt power source.

Oh ok this is starting to make some sense to me now. It must be wired up wrong somewhere

[jtrichard]

Originally Posted by 62stepside longbox

Oh ok this is starting to make some sense to me now. It must be wired up wrong somewhere

Now you got it and are heading the right direction

[spookylynx]

so does the sending unit itself need to be grounded? Or is it grounded through the steel tank. Mine just has one terminal in the center that goes to the gauge.

[62stepside longbox]

Originally Posted by spookylynx

so does the sending unit itself need to be grounded? Or is it grounded through the steel tank. Mine just has one terminal in the center that goes to the gauge.

It has two terminals, one that goes to the little transmitter part and one that is a ground

[62stepside longbox]

Thanks for all the help everyone. I got the problem solved today. It turns out when I was tracing the wire from the gauge It went behind the steering column and another brown wire came out from behind the column so I assumed that was it, but I tested for continuity and got nothing so I traced the wire more closely and found it was a different wire so I tested for continuity and bingo! That was it and now my gauge works

[Tazimafied]

Very nice! Great success! What does the other brown wire go to? Doesn't sound like a factory installed wire.

[62stepside longbox]

Originally Posted by Tazimafied

Very nice! Great success! What does the other brown wire go to? Doesn't sound like a factory installed wire.

I believe the wire was installed by the PO when he rigged up his own garbage reverse lights. All the stuff he did to the electrical looks like it was done by a 6 year old, includes wire and electrical tape balled up under the dash

[Rust-O-Matic]

Ha! Sounds like the same guy might have wired my truck. A 6 year old could have probably done a better job. Glad you got it worked out, and I appreciate the description of how the wiring is supposed to work. I need to look at mine as well.

When I was replacing my fuel tank's sending unit, I also realized the filler neck had been replaced with a gatorade bottle with hose clamps around each end. Talk about low budget ingenuity...