Fuel gauge wiring - Team Camaro Tech
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post #1 of 9 (permalink) Old Mar 14th, 09, 09:07 AM Thread Starter
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Fuel gauge wiring

Ok, read most of the post and sticky's about this....I have a 68 camaro with the gauge at the cluster (next to spedo) all original.....I have checked the sending unit at the tank (without dropping the tank) by unplugging the tan wire, ohms to ground read 25, which is about what I thought I should have in the tank (1/4 or less, since the gauge has not been hooked up for quite some time.)

So, I checked at the gauge cluster, took out the connector and tested the wire, it read 24 ohms grounded up there. so I dont think its the sending unit.?

I've tried to also disconnect the tan wire at the trunk, put the IGN on and no movement of the gauge. However, when I plug the wire back in (at the trunk) and turn the IGN on, gauge moves to E....

That being said....I have not totally finished the wiring (painless 18 circuit setup) of the entire car circuits (ie: heater, ac, rear tail section, etc). I have also yet to finish putting in the gauge cluster as I have to play around with the heating/ac ducting, etc up under/in the dash.....

Could that possibly be where I am having problems? (lack of ground circuits?) or can I diagnose the problem without the entire wiring loom being installed and properly grounded?

Any help is always appreciated

Anything worth doing is worth overdoing...a little's good, more's better, and too much is just enough
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post #2 of 9 (permalink) Old Mar 14th, 09, 09:23 AM
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Re: Fuel gauge wiring

Sending unit appears to be reading correct. You might use a higher resistance scale, to give the meter leads more available voltage, and go across the meter itself to see if it moves.

Make sure the cluster is grounded and a full battery voltage is available to the gauge.
You might plug in a 100 ohm resistor to the tan wire and to ground to see if the gauge will read full.

Let us know.

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post #3 of 9 (permalink) Old Mar 14th, 09, 09:42 AM Thread Starter
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Re: Fuel gauge wiring

Thanks Everett, I will try that, hopefully tomorrow (maybe if I sneak out into the garage while she is on the phone )and post whats going on....as its the wifes birthday today...so no working on the "other" woman in my life today...

A happy wife makes a happy house....and a happy house gets me into the garage to work!!

Anything worth doing is worth overdoing...a little's good, more's better, and too much is just enough
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post #4 of 9 (permalink) Old Mar 14th, 09, 10:10 AM Thread Starter
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Re: Fuel gauge wiring

OK, snuck out and grounded the cluster. (wifes STILL on the phone...... ) Gauge went past full. wired back the tan wire, tuned on IGN and reading went again to empty. Checked the voltage at the tan wire in the trunk....getting 8.5 volts. Is that enough at the trunk?

Voltage at the gauge reads 11.88. (also 11.88 at the lead wire into the cluster.) cleaned up the ground at the tank (again) and went to check the ohms....got a low battery warning on the dmm. Need to change that! soooooo?????

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post #5 of 9 (permalink) Old Mar 14th, 09, 03:15 PM
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Re: Fuel gauge wiring

Instead of measuring individual voltages try reading the voltage drop. For example, the reading between the sender ground wire and the guage ground should be very low with the circuit powered up. Same thing for power, although I'd be inclinded to measure from the gauges power source to the battery (+).

The 8.5 volts is difficult to reference, but it's probably fine. It depends on how much fuel you have in your tank. There probably aren't too many people that have measured that voltage to give you a reference. The the main contraints are 90 ohms = F and 0 ohms = E.

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post #6 of 9 (permalink) Old Mar 15th, 09, 09:39 AM Thread Starter
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Re: Fuel gauge wiring

Quote:
Originally Posted by dnult View Post
The 8.5 volts is difficult to reference, but it's probably fine. It depends on how much fuel you have in your tank. There probably aren't too many people that have measured that voltage to give you a reference. The the main contraints are 90 ohms = F and 0 ohms = E.
Thats at the tan wire connector in the trunk. Not sure if thats enough voltage for the sender. Haven't dropped the tank either.....yet....so was questioning if I really need to do that to check directly at the sender.

Gotta get the taxes done this week, so this projects gotta wait till next weekend, but any help is always appreciated.

Anything worth doing is worth overdoing...a little's good, more's better, and too much is just enough
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post #7 of 9 (permalink) Old Mar 15th, 09, 09:44 AM
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Re: Fuel gauge wiring

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Originally Posted by gramps68 View Post
Thats at the tan wire connector in the trunk. Not sure if thats enough voltage for the sender...
The tan wire isn't a power supply for the float sender perse. That 8.5 volts will vary depending on the position of the float. So don't get hung up on it. Resistance vs meter reading is what matters here. This is a voltage divider circuit here and the fuel gauge is translating current flow through the sending unit into a meter reading.

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post #8 of 9 (permalink) Old Mar 15th, 09, 10:03 AM
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Re: Fuel gauge wiring

I agree with Dave, fuel meter works on current going through it. The amount of resistance 'seen' at the sending unit determines the amount of current flow through the meter, the meter turns it into an indication; 0 ohms = empty, max ohms = full.

Easiest troubleshooting is to get two resistors, 45 ohm or 50 ohm, since may be a stock value. Any wattage size is good, 1/4, 1/2, or 1 watt will be fine. Radio Shack or an electronics supply house.

Two resistors in series is full tank.
One resistor in series is half tank.
Two resistors in parallel is quarter tank.
Resistors will be hooked up with one lead(s) to the tan wire and other resistor lead(s) hooked to ground.

Agree, happy wife, happy times for the husband(servant)......Yes, Master.......we always have the last words "Yes, Dear."

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post #9 of 9 (permalink) Old Mar 15th, 09, 10:27 AM Thread Starter
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Re: Fuel gauge wiring

Quote:
Originally Posted by Everett#2390 View Post
Agree, happy wife, happy times for the husband(servant)......Yes, Master.......we always have the last words "Yes, Dear."
Aint that the truth!!!

I'll give it a shot this weekend, hopefully, if I can get the taxes done.....

Anything worth doing is worth overdoing...a little's good, more's better, and too much is just enough
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