Quick Fuel Gauge question

[csjr]

I'm fixing my stock fuel gauge once and for all. I don't expect digital accuracy, but I'd like to at least get stock performance. Since I've bought the truck it has never worked properly--always a lot lower than reality and reads empty when it should say 3/4 tank.

Anyway, I checked IVR on back of gauge cluster--pulsing power per test light and voltmeter. I checked wiring all the way back to tank--pulsing brightly with test light. I grounded power back by tank and gauge pegs full as expected; therefore, I conclude good IVR and good gauge. I take off the ground and test resistance with ohm-meter....it's jumping all over on my lowest scale (200) so I'm assuming I'm getting pulsed power through the sender at the ground. Now, I could not find a battery to chassis ground on my truck. PO has rewired (what an F-ing mess) and I see ground straps from chassis to body and engine. Is this critical for gauge function? I'm thinking I can add a strap from battery to same place on front fender well where body to chassis ground terminates. I'm thinking this gets me to chassis. There's a massive ground cable from battery to engine. Any info would be greatly appreciated. Getting the fuel gauge to work would double my functional gauge count.....

 

[oleguy74]

a good ground is nessary.if you grounded sender wire at tank from frame and gauge pegs you have a good ground.get a 25 ohmres,a 10 ohm res,and a 73 ohm res.a couple pieces of #14 wire and 4 alagator clips .make up two clipcords.one clip wire to ground and one side of res and other side of res connect to sender wire to gauge.10 ohms full, 25 ohms 1/2, 73 ohms empty.if you have single tank,you won't have to bother with switch.

 

[csjr]

Thanks oleguy. This is a great way to test what's up. I know I want to replace all the gauges with custom Autometer, but it would be nice to know something in the meantime. My speedo gear spun and needs resetting in the Tcase, so I can't go by miles any more....

 

[DirtDonk]

When my gauges read low, I had to re-adjust the sending units. Doing that fixed the whole issue.

Since you have ground straps from the engine to the frame and body, your are in effect, well grounded. I still like to see direct grounds from the battery though, just because.
The factory had the main ground cable grounded to the inner fender facing the alternator, just adjacent to the starter relay on most. Probably the same way on your '73. Very likely one or two small (1/4" or so?) holes in the inner fender up near the top.

You can run a jumper from the negative straight to one of the holes using a sheet metal screw. Even though you're grounded, it wouldn't hurt.
Another good one is to run a strap/wire from the gauge cluster to the dash or other known good ground. It should already be well-grounded through the four mounting screws, but it seems that a lot of people have grounding issues to the gauges anyway.
No such thing as too many grounds.

Paul