Temp Guage problems.

[leddzepp]

My temp guage worked great up until about a week ago. Now when I turn the key on, it goes all the way over to Hot and stays there. I changed the sending unit, but that did not solve the problem. Is it time to get a new guage, or can there be some other problem? Thanks!

[jef5150]

old problem cant help but possible causes for the new sending unit is

if you buy a sending unit for "idiot" light and use it on a "gauge" it will peg out

dont use teflon tape, the unit grounds to the block.

jeff

[Longhorn Man]

odds are, the green wire that goes tothe sending unit is melted onto the exhaust manifold, or maybe chavfed and grounded out.
The above comment of thread tape is correct. The sender is a pipe fitting which is a tepered fitting, designed to prevent leaks without the use of sealers.

[clay68c10]

You could also have a burnt out the resistor on the back of the gauge. Not common, but possible.

[dwcsr]

I had a similar issue, on my 72. It didn't work at all when i got the truck and I changed the temp sender and it pegged. change everything from the sender to the dash and still pegged, Removed the idiot light bulb for the TEMP light and it worked fine.

[VetteVet]

I'm lazy
http://www.6066gmcguy.org/Electrical-02.htm

[red71cheyenne]

Had a similar prob in the Blazer, was the ground wire for the dash. Just had to get it grounded better and all good.

[BLACK AND BLUE 67-72]

Sounds like the wire is grounding out on something, mine did this and it was melted to the exhaust manifold. As far as the teflon tape not letting it ground then why do most of the new senders have it already on them, the threads will cut through the tape and it will ground. The threads are what they call tapered pipe but you still have to use a sealant of some sort to make it not leak, hence the names pipe tape, pipe dope, pipe sealant, etc...

[468chvy]

first off the missconception about using tape or dope to seal a fitting is wrong, guys think that the tape or dope actually does seal, as a steamfitter, I know the proper use of tape or dope is to lubricate the threads so you can tighten them together, and the taper of the threads is supposed to make them seal, not saying tape or dope wont prevent a leak, but just the proper and primary use is for lubrication,

[leddzepp]

Well, I traced the wire from the sending unit to the guage, and no problems with it touching anything or being exposed. I replaced the guage and still have the same problem. I have now checked the wire, and replaced both the sending unit and the guage...what's next, the resistor on the back of the temp guage? i do not think there is a problem with the circuit board on the back, as all of the other guages work fine still.

[leddzepp]

Originally Posted by red71cheyenne

Had a similar prob in the Blazer, was the ground wire for the dash. Just had to get it grounded better and all good.

Is there another wire that is supposed to connect to the back of the guage? All I see is the two places where the circuit borad fits onto.

[red71cheyenne]

Coming off the wiring harness that plugs into the back of the dash is a black ground wire with a little "U" shaped connector. This is pushed onto the metal of the dash itself and serves as the return path for your guages. If you don't have some bare metal for it to ground on, you will eventually have guage issues.

[jef5150]

dash ground




jeff

[leddzepp]

Originally Posted by jef5150

dash ground




jeff

Sweet pic...yup, that piece is grounded perfectly!

[red71cheyenne]

Hmmm, well then, what did your resistor read on the back of the guage? Are you sure the nuts that tighten the printed board to the guage are snug? Any open runs on it? I know you said you thought it was good, but may need to verify. Also do a continuity test from the sender to the plug at the dash and make sure the wire isn't open.

Great Pic jef5150, don't have access to that over here....

[leddzepp]

OK, it seems to be working now. I installed a new guage, and I noticed the bottom terminal being marked G for ground I assume. This is also where one of the resistor ends connects to. On the original guage, there was nothing else present. So I attached a separate ground wire to this terminal, and BAM it went back down to C and then gradually went up as I ran the truck. Does this mean the aftermarket temp guage requires an external, separate ground independent of all of the other guages in the cluster? And I assume the factory original temp guage does not?

[red71cheyenne]

Yep, thats what it means. I thought you were using the stock temp guage. If you were at the beginning of this, then you still have a lack of ground issue in the stock guage. Could be the printed board, the ground wire or the resistor.

[leddzepp]

I tried the new guage and ended up with the same problem until I attached a separate ground wire. Since it was marked G it must require an external ground attached there. On the factory guage there was never an external wire attached to it, nor was it marked for one. With the factory guage, I attached a separate ground wire to that terminal and it still stayed all the way over at H. None of the other guages in my panel have ever given me a problem and I have had the truck for YEARS. So I am deducing from this that the factory guage went bad somehow. The old resistor is on the new guage, as well as both of the tabs from the circuit board and it works!

[jef5150]

Originally Posted by red71cheyenne

Great Pic jef5150, don't have access to that over here....

ive had it for while.....dash lights wont work without it either.


jeff

[jef5150]

heres the stock wiring,got it off the board




jeff

[leddzepp]

Thanks for the pic Jeff! I am pretty sure the original guage went bad, as it worked perfect up until a couple days ago. Obviously if it worked, then it was properly grounded (to the cluster) to begin with...how would the ground suddenly stop? Even when I added a ground wire to that post on the factory guage, it STILL went to H, and the new guage worked properly.

[red71cheyenne]

Could be that the nut for that terminal worked a little loose when you swapped guages or something. I had issues with mine too in the Blazer when I put it in. Mine was the black wire not making contact with the dash. The one in my 71 still doesn't work, but thats due to my own terrible wiring problems. I put a voltmeter in the stock ammeter location and that changed the wiring some. Temp guage still don't work in that one. Maybe when I get home from Japan I'll work on it some. Nah, hell, I'm just gonna drive it!