Re: Hooking the fuel gauge up?
Well, to answer your question, the wire from the tank (sending unit) is a tan wire that goes to a connector in the truck, from there up to the left terminal (viewed from rear) on gauge, still as a tan wire. If you ground the tan wire, then the fuel gauge will read empty. I think you need to run through the tests below to get ahandle on where your problem is..................
Here's the short course on checking gauge and sending unit:
To check gauge wiring, viewed from rear -
* Pink wire on right is 12v from key switch. Confirm with test light
* Tan wire on left goes to sending unit
* Center lug needs good ground. Be sure it's grounded
To thoroughly test gauge ---------------------
Disconnect tan wire, turn key on, gauge should read full
Connect jumper wire from sending unit (left) terminal to ground, gauge should read empty (with key ON)
Now, for a definitive test, go get a 40 ohm resistor from Radio Shack and add that into the jumper wire line, and go from sending unit terminal to ground. With key ON, gauge should read about 3/8 of tank.
If you're reading 3/8 tank with that 40 ohm resistor in the jumper wire (and key switch ON), then your gauge is fine.
Now check sending unit---------------
First, make sure wiring looks good. Check ground connection (black wire) and clean.
You can do this on car but you need ohm meter. Go to inside of trunk at center and disconnect gauge (tan) wire. Use ohm meter and take reading from sending unit wire to a good ground. If tank is full it should be about 90 ohms. If tank is bone dry it would read about zero. If it's reading, say, 125 ohms or more, it's no good.
Confirm bad sending unit by draining (or adding) 5 gallons of gas and taking another ohms reading. If you had initial ohms reading of 80 (close to full tank) and you drain 5 gallons of gas, then your ohms reading would drop considerably, maybe to about 55. If your initial ohms reading is close to zero (empty tank) than ADD 5 gallons and it should be around 40 ohms. If you are adding (or draining) gas and the ohms reading is NOT changing, then your sending unit needs to be replaced, or the sending unit wiring simply may be bad (broken wire or bad ground)..................
Dave F. in Rhode Island
'68 Camaro SS Accel DFI 454 (SOLD - I'm a boring Corvette owner now)
Bought my first big-block Chevy in 1970