1984 GMC - Dual tanks and Fuel Gauge

[ctandc]

I'll try to remember to take some pictures to post - but recently got a '84 GMC Sierra Classic 4x4 Short bed. The fuel gauge was stuck on a bit over 1/4 tank - even when the LH tank (was running on that one) was full. Bought a used gauge off Ebay, and now the gauge 'moves' and actually you can tell the tank switch etc works via the new gauge ....but the new gauge jumps around. Especially when RPM's climb.

I'm figuring it's a ground from one or both of the senders maybe? Before I break out the wiring diagram - anyone had experience with a gas gauge behaving like this? Anyone know where - at least general vicinity - the grounds for the tank senders are? I was hoping a good clean and reattach might help.

Still constantly surprised how good of shape this truck is in. Papers and warranty on a the 700R4 that was rebuilt 6 months ago ($1800 worth) and they added a tranny cooler at the same time. Engine is a Jasper engine (305 originally - guessing this is a 305 haven't checked the numbers yet) with 50-60K on it.

Painted in the late 90's or so. Driver's outer rocker is gone. No floor pan or cab support rot. Cab corners look okay too. Only other thing is some rot in the bed wheel arches - figure patches will do nicely.

Ironing out some small things so the truck can be driven and well, used as a truck.

Only 'urgent' thing is dealing with a bench seat where the driver's side springs and / or foam is basically worn slam out. I'm 6'3" and if I don't put a firm pillow on the the seat when I'm driving, I can barely see over the dash LOL.

Thanks in advance for any guidance.