Finn5033

Hello, I have a 1970 cutlass supreme. The gas guage is buried past full down by the heat light. It does not move when I fill up or when the car is turned off. I checked the ground for the sender and cleaned that up to no avail. I decided to order a new sending unit with float. Is there anything else I could try before I replace that? Any thought would be appreciated. Thank you

jaunty75

A fuel gauge that pegs past the Full mark indicates an open circuit. Checking the ground from the sending unit was good, but you need to check the line all the way from the gauge to the rear of the car.

There is likely a connector somewhere in the area around the rear license plate, perhaps behind the trunk latch area inside the trunk, where the wire coming from the sending unit connects to the wiring going to the gauge. Make sure this connection is good.

If you open this connection and ground the side coming from the gauge, the needle should peg to Empty. If that happens (key must be on), then there is nothing wrong with the gauge itself or the wiring from the gauge to the rear of the car. If it doesn't peg on E, then there is still an open in the wire between the rear and front of the car. Time to start tracing some wires!

Finn5033

Thanks for the tip.

oldgold

Hi guys,new to forum.I have a 71 cutlass thats having problems like Finn 5033 has.Guage pegs pass full & stays there.As per Jaunty 75 I did what he suggested and everything worked like he said.I pulled fuel tank and found the ground wire was broken.(prior owner puy in new trunk pan and disregarded the ground) I put in a new ground wire and still no guage response,it's still on full +.Could it be the sender unit itself ?.The sender unit is a single tube type,no return tube.Thanks for any help,Tom.

jaunty75

Yes. Once you've eliminated bad wiring as a cause and made sure the dash gauge itself is working ok, the only thing left is the sending unit.

It could also be the wire from the sending unit if you can check that without dropping the tank. You want to be sure it's properly connected to the sending unit and not broken somewhere between there and the rear of the car where it connects to the wire coming from the gauge.

As I said, make sure the wiring is complete and intact throughout, and if the gauge still doesn't work, the sending unit is next.

oldgold

Thanks for reply Jaunty 75.But i did have tank out already and all wires were there except for broken ground.So i guess I have to buy a new sending unit.

jaunty75

Sounds like it. But getting the tank out so you can get at the darn thing is 99% of the effort, at least in my case. Once the tank is out, it's pretty simple to remove the old sending unit and put in a new one.

oldgold

Well Jaunty 75 pat yourself on the back.I changed the Sending unit and everything works.Thanks for input,Oldgold.

jaunty75

Thanks, but you did all the work!

I had to remove the tank twice on my car ('67 Delta 88). The first time, I tried repairing the existing sending unit, but it still didn't work well, so the second time (which I also wanted to be the last time) I put in a new sending unit. In my case, no reproduction unit is available, but I found out that units for a '72 Buick LeSabre, which are made new (and which likely also fit other '72 full-size GM cars, but I ordered it off of a Buick parts list) are a drop-in replacement, and it has worked fine.