Hooking the fuel gauge up? - Team Camaro Tech
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post #1 of 3 (permalink) Old Oct 12th, 06, 08:39 PM Thread Starter
Join Date: Oct 2006
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Hooking the fuel gauge up?

Ok here is another question I am facing on the 67. The fuel gauge wasn't hooked up when I bought the car and of course, wanted it working because I don't like just guessing with the big block drinking gas. There is a wire that comes out of the center of the floor board that reaches easily to the tank, but not tied into anything. Coming off the top of the tank(without having dropped the tank) are two wires, one obviously a ground and another that seems like it would be tied into the fuel gauge up front. But when I ground the one wire and tie the other one in, no fuel reading on the gauge like always. Are these the correct two wires to be hooking together or is there another one that comes from up front that I need to look for?

Thanks for all the help.
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post #2 of 3 (permalink) Old Oct 12th, 06, 09:11 PM
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Location: Southeast PA
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Re: Hooking the fuel gauge up?

The sending unit wire to the gauge is tan, so if you are hooking a tan coming from the tank to a tan wire in the rear light harness, the connection up at the dash harness and instrument cluster is good, and the sending unit ground is good and still you get no reading, the sending unit itself is probably bad.

There are a lot of "ifs" there because I'm not sure I understand what you described, as far as "a wire that comes out of the center of the floor board that reaches easily to the tank." The wire to the gauge is part of the rear lighting harness, and there is a connector behind the trunk latch brace, from which the wire runs down through the trunk floor, across the top of the tank, and into the sending unit. Sending unit grounds through a short wire to the trunk pan reinforcement rail on the passenger side.

69 'vert project big block/TKO 600 RR
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post #3 of 3 (permalink) Old Oct 17th, 06, 05:32 AM
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Location: Rhode Island
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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
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