Why is my fuel guage grounding out?

I'm using the original fuel gauge for my truck, I ran a new wiring harness and and put in a new tank with a sending unit. But once I got everything hooked up I noticed that anytime the gauge cluster is hooked up and touches a grounded part of the vehicle, the gauge automatically goes to fuel. Does anybody out there have an idea of whats happening?

 

Was your car originally positive ground?

 

Have no idea. It's a 46 chevy stylemaster. I don't know which years fell under positive grounds. How would I fix the problem if it was?

 

I know it used to be a 6 volt system, but now I have a new harness and a sbc in it. So it's running 12 volts. I had to get plastic parking light sockets, cause the charge would keep blowing fuses when they ground out.

 

No, the car should have originally been a negative ground. GMCs had positive ground on their 6 volt setups.

 

Does anyone else have this problem or is my lack of electrical knowledge that should be examined. It's a summit 18 circuit Universal wring harness.

 

Did you wire in a voltage drop to the gauge? HRP

 

Yep, have the 12v source to the voltage drop and voltage drop to the gauge, and the sender wired to the gauge.

 

Bad sending unit? See it all the time.

Jon

 

It sounds like you are completing the circuit by intalling (grounding) the gauge and it sounds like you may have a bad sending unit. Does it still do it if you remove the wire from the sending unit? On a properly working gauge you can remove the wire from the sender, ground it, and it will read full. If the sender is ok you may have a short somewhere in that wire.

 

The funny thing about it is When I hook up the sender wire, and the 12v source to the gauge then place it int he dash the lights in the unit glow slightly. but the dash lights are not turned on. To me it sounds like I've got a positive wire charging the dash, but I've been over them and I can't find anything.

 

Oh and the gauge does it without the sender hooked up. From empty to full, as soon as I place it in the dash.

 

Does the post for the sender wire go through the housing for the gauge? Is there any isolator washers or bushings missing? Check the cont between the post and the gauge body. I think if you have cont the unit is grounding internally.

 

The post does go through the housing for the gauge! I know for a fact there is no isolator washers on it. I'll be sure to add some and see if that works.

 

Try a piece of rubber tubing or heatshrink around the post to protect it.....

 

Good idea, thanks for the advice

 

Do you have a ground wire from the sender to the frame? HRP

 

Also make sure the new sending is the same ohm's as the orginal?

 

Well- did the post contacting fix solve your issue? Don't leave us in the dark....

 

Long shot but it happened to me... Check your wires going through the fire wall. I had a wire (new) that got a cut in it and was causing a similar problem. Damn i hate electrical problems..good luck

 

check your sending unit wire it might be touching the body i know it happened to me

 

Most have been stated but this is from the troubleshooting section of my fuel sender:

TROUBLE SHOOTING HINTS
SYMPTOM: Meter pointer stays above FULL mark when the Ignition switch is turned on.
1) Full tank of Gas.
2) Water in fuel tank.
3) SEND and NEG wires reversed on Sending Unit.
4) Meter not grounded properly.
5) SEND wire is touching NEG terminal or wiring
6) Center rod on fuel units touching the outside tube.
7) Unit not calibrated.

Note this is for a resistance type sending unit, not a float(which explains #2 & #6 if you were wondering).
http://livorsi.com/pdf/GSFLC3-GSWLC3.pdf

 

Make sure your sill plate screws are not pinching the wire for the sender.

 

Dammit man!,,did you ever figure out what the problem is/was,,,,you could at least tell us! HRP

 

ditto what KJSR said. I had the same thing happen to my temp and oil pressure gauges, but ONLY when I tightened the mounting nuts to the back of the dash, worked fine when not mounted in the dash!!??!! This happened with brand new harness, brand new gauges. Insulated the metal mounting bracket on the gauge cluster, so it would not touch the metal dashboard, now I'm a happy guy.

 

alright, finally got the dash back into place. After getting some sound advice from all the fellow Hambers I went ahead and took the panel off and found that the post in the back did not have isolator washers attached. So I went ahead and placed some on the posts, reconnected the wires and took KJSR's advice with the shrink wrap. It looks like we have a winner! The gauge is reading the correct amount. So now I just have to run it for a while and see if the fuel level goes down. Hopefully this weekend.

Thanks again guys, and skidsteer, how did you insulate the mounting bracket?

 

Here is my issue. I have a '48 Chevy, but the entire driveline is an S-10 of some sort except the motor. All 12V new harness. I am still sorting ground issues out and other electrical shit. So anyway. I am running an S-10 Blazer tank in a pick-up frame. (some say HUH who cares!) The after market senders are so close to the floor in the back that they scratched through enough paint to bridge. Check all your posts, and connections. I hate electrical.

 

I hate electrical also. Everything needs to be just right. It's double shitty when your in a garage and it's 90º out under a car, fiddling with wiring. Nothing says rage like that.

 

Glad to hear it worked out for you!