Gas gauge reading incorrectly on '62 Skylark 215 V8

[Topcot]

My gas gauge on my '62 215 V8 Skylark registers the correct reading when the engine is off (ignition off) and reads full when the car is running. Any suggestions as to what might cause this and how to fix it? From what I can tell, to get to the sending unit means dropping the gas tank and that as we all know is much work.

[BigRivy]

If it's changing like you say it's probably a wiring problem, not the sender in the tank. Trace the wiring under the car and look for problems like a bare or corroded wire. It could also be a bad ground in the dash etc. Something is feeding the gauge a little juice when the car is running that shouldn't. Try to find a wiring diagram and start checking stuff.

[Topcot]

Thanks. I'll check all of the wiring as this is what I thought was happening. The actual dash gauge is difficult to reach so that is an issue. Thanks for the input.

[FoxProGT]

I had the same issue in my 62 special... In my case it was a bad ground at the sending unit.

Dropping the tank is work but was a lot easier then i thought it would be. It was pretty rusty down under the tank area. I cleaned up as much of the rust as possible. The clean up worked but i also ended up hooking up a separate ground wire on one of the sending unit bolts to a nut on the body. The gauge works great now.

The easiest thing you could try is to take off the 2 tank straps and sand the rust off of them The bolts that hold the straps on should be cleaned off too. The other end of the straps kind of clip or slide in a slot in the body. That area should be cleaned off as well. You would need to prop the tank up with a block or bricks when you take the straps off obviously :P

[njlimbaugh]

Sometimes an easy fix is simply running a ground wire from the tank to the chassis. Test this with a jumper wire to confirm the problem.

[Topcot]

Thanks to all for the valuable information. I'm going with the simplest first and then moving on to dropping the tank.

[WildKitty]

In the 64s, there's a plate on the ledge where the spare tire goes - gives you access to the fuel sending unit
dunno about the skylark, my 64s are a wildcat and a lesabre

[FoxProGT]

There are 2 plates in the trunk of my special. Most likely there in the skylark too but they do not lead to the sending unit. Im not really sure what there for besides sweeping out dirt and debris from the trunk.

[WildKitty]

OK guys, before I made another appointment with my shrink, I went out and looked in the trunk of the Wildcat. the plate to get to the fuel sending unit is pretty well sealed over, the bracket that holds the spare tire in place is WELDED, the plate is held in place with a few hex head sheet metal screws + lots of water proofing gunk.

dunno about the special or the skylark, but the space UP behind the back seat, under the package tray, is where the spare goes in the wildcat and lesabre. I put a "saddle tank" in the trunk of the lesabre (extra 15-16gals). with the "little" 300, should get about 600 miles onna fillup.

[WildKitty]

It would be nice to know if the problem was traced and resolved, and how