fuel gauge or sending unit?
 

Not sure weather the gauge is bad or sending unit can someone please help me determine by using volt meter. I tried to look for the wire coming from the sending unit but I got under the car and didn't see any. Do I have to drop the tank? Any suggestion help would be greatly appreciated.

GM fuel gauges are 90 ohms read with a meter to ground. If you open the wire with a good sending unit the gauge should go to empty. If you short the wire to the gauge to ground the gauge should go to full.
If you can't find the wire then you'll have to drop the tank.

I was hoping I can do this hehind the fuel gauge. I thought I may be able to read the sending unit throught the 3 prong that plugs hehind the gauge. Thank you for your reply.

If you can pull the 3 prong and figure out which wire is which, then you could check it there. I don't have a diagram for a 1st gen wiring harness, but if you figure out which is to the sending unit you could try to ground the wire while lleaving it attached to the gauge. Then you could also check to ensure there's 12v. power at the gauge too.

Actually, GM works the opposite of that. If the sending unit gauge wire is grounded to the body, the gauge will peg to empty. If the wire is broken or disconnected, the gauge will peg to full. This is provided both the gauge and sending unit are hooked up and working correctly. There are two wires to the sending unit. A black one that grounds the body of the sending unit, and a tan one that goes to the gauge. The sending unit is on the top of the tank, but you can trace those wires down the side. What does your gas gauge do? If you get no deflection when you turn the key on and off, the problem is with the gauge itself, or the wire supply/connections at the gauge.

Are you positive? Because I just went out to the Suburban and tested this since it's got a plugin connection. If I unplug it the gauge goes to empty, and when I ground the wire from the gauge to the frame it goes to full.
Haven't tried the Camaro to see if it's the same, but I thought all GM's were this way?

Not all cats are skinned the same: Troubleshoot Fuel Gauge

On my Camaro if the wire from the sending unit isn't hooked up my gauge goes to full
Same on my C10

I'm really confused now. Not sure why the Burb does the reverse, and from others I've talked to with old Suburbans their gauges work the same. Suburbans have a nice little single wire plug right at the tank, so very easy to service or check.

I appreciate all the replies but somebody scholl the nubee on how to ground it!
Also this is how my gauge look key on or off.

http://img.photobucket.com/albums/v3...908_060031.jpg