Factory Temp Gauge & Fuel Gauge Not Working

[Harrison.]

I converted my warning light dash to factory gauges using a factory wiring diagram and reproduction gauges from LMC (which I'm not ruling out is the problem). However, I am having issues with both.

The temp gauge is on 0 with the ignition off but as soon as I cut the key on it slowly goes past high. The resistance between the dark green terminal on the instrument cluster to the temp sender is .2ohms. If I take a reading between the temp sending unit and ground it is .364ohms at 180 degrees. Resistance between the dark green terminal at the instrument cluster and ground is 1.151ohms. I read other threads and ran a ground from the cab to the bottom peg on the gauge but still have the same issue. I've still got the instructions for the new gauge but it says not to put the factory resistor in place, I still tried it and with it in it doesn't move off of 0. What am I missing? Maybe I have the wrong temp sending unit? I did watch the ohms as the truck warmed up and it continuously changed as it warmed up.

The fuel gauge is also inop. If I put one side on 12+ and the other to ground it stays on empty but the tank is full and even grounding it directly to the fuel sending unit it does not move. Any ideas?

Thanks!

[custom10nut]

Check your grounds

[dmjlambert]

"reading between the temp sending unit and ground it is .364ohms at 180 degrees." sounds like incorrect or defective sender to me. Here is the resistance chart, should be about 110 ohms at 180 degrees.

Posted by davepl here:
http://67-72chevytrucks.com/vboard/s...53#post7680753
The correct sender is GM part number 12334869, AC Delco number G1852. Looks like this:

[Sheepdip]

Like Custom 10 says...eliminate the ground issue, it's easy and cheap to run a wire from the battery neg post to your tank, gauge or whatever to confirm grounding.

About 90% of electrical problems are grounding issues.

[Harrison.]

I didn't get a chance to pull my seat out and ground the fuel sending unit, however I did build a small ground wiring harness for the gauge cluster and put the factory resistor back in again (even though the instructions said otherwise) and the temp gauge finally gives me a reading. However, it's almost on HOT between 180-190 degrees (it's a big block). Could that be due to the sender? Or is this just going to be how it reads?



Preferably I'd like it to read more in the middle at operating temp.

[randy500]

Why isnt the printed circuit grounded to the metal guage backing with the missing screws at the top left and right?

Put those screws in, they are needed to ground the cluster....and get rid of that crappy ground wire you rigged up. Then verify the black wire (clip) is attached to the lower dash, thats your actual ground.

Nothing on these trucks needs an extra ground but it does need the grounds designed into the wiring system.

[LockDoc]

-
Here is a picture of the factory ground that Randy mentioned. Remove it and put it back on to make sure it is making contact.

LockDoc

[randy500]

Thanks locdoc....and for everyone adding grounds...quit it, that wire is a direct ground from the guage connector to the lower dash. The clip has sharp teeth, make sure they cut through the paint and thats all thats needed.

One of the problems is those painted rear guage panels, gm didnt paint most of them because the guages get grounded through the guage attachment screws into the back panels which are grounded by the 2 missing screws, which gets its ground through the black wire.

[tim_mc]

Attaching a pin-out diagram showing the difference between idiot light and gauge clusters just for reference in the thread, and to double-check your pin-outs on the cluster connector.

[BigBird05]

Randy500 The grounds on a 50 yr old truck are ****ty. I remove the old scratch ground and install a ring terminal with a star washer and a screw!

[Sheepdip]

Originally Posted by BigBird05

Randy500 The grounds on a 50 yr old truck are ****ty. I remove the old scratch ground and install a ring terminal with a star washer and a screw!

[randy500]

Adding grounds and star washers is foolish, od you pay for the fuel system cleaner at the gas pump too?

[Sheepdip]

Originally Posted by randy500

Adding grounds and star washers is foolish, od you pay for the fuel system cleaner at the gas pump too?

Trying to figure out what fuel system cleaner has to do with a good solid ground?...but then again I don't get out at intersections and argue with a stop sign.

[Daaaanz67]

Anything that has to do with electricity and grounds, I live and die by star washers. It kind of has the same effects as that scratchy ground clip. Not trying to argue on anything here just simple facts.

[71gmcC15]

If you whant to add grounds go for it. It dont hurt anything. Nothing can ever have to good of a ground in my opinion. Yes the way the factory did should work. But it also 50 years old. And half the grounds are probably shot.

[MySons68C20]

[randy500]

All this talk about grounds is coming from people that don't know a thing about the circuits involved.
Adding grounds is akin to changing parts to see if it fixes the problem, it wastes time and money.
The circuit should be traced and fixed.

What im saying is quit with all the adding grounds and find the fault in the current system, if you can do that you can fix any circuit.

Almost every week there is a thread about why my fuel guage or temp guage dont work or tail light, blinkers or front turn signals dont work
Yes its always the grounds but adding wires is almost never the solution.

In this case the printed circuit is not grounded to the guage metal backing plate, putting the screws in will fix the problem. In may cluster ground problems the backing plate gets painted and looses ground in the process, guages are also installed incorrectly without being grounded to the backing plate.

Test the circuit with an added temporary ground wire but then go ahead and repair the circuit.

Adding grounds just clutters up stuff and leaves the next owner to fix prior owners mistakes.

Honestly if you dont know the circuit then please don't post, i and others are trying to teach what it takes to fix the circuit not just add band aides or redundant stuff.

[71gmcC15]

I never sade keep the grounds. Just use them to see if that's the problem. Then yes fix it right. And I had a thread on one of my blikers that did not work. Gess what it was not the ground. It was no power for the signel wire. So it's not always the ground. But always asume its the ground. There is a difference.

[BigBird05]

Well if you want to make your truck run better don't add any of that nasty cleaner at the pump. LOL.

I agree with Randy500 in that the wiring can be done per the factory wiring schematics on any vehicle and, from a purist’s standpoint (of which I am one) I agree. With that said, I have used jumper grounds to isolate a problem (and even left them in for the sake of convenience and avoiding frustration).