LMC Temp Gauge pointing to H

[Hardway]

I am back to the single event that started the my wiring harness replacement. Ever since I bought the truck back in May the gauge has pointed to H. I bought a new gauge from LMC and a new printed circuit board. Installed the gauge per the instructions, not using the resistors, just places the insulator tabs in the cross configuration. Put it all back together, still points to H as soon as I turn the key. Now I have a new Painless Harness in the truck, I made sure I used the temp gauge sending it wire and not the light, bought a correct slide/clip connector for it, turn the key, and it goes to H immediately. With the connector unplugged it goes to H. I bought a new sending unit, grounded it to the truck, hooked the connector to it, still at H. At the connector with the key on I have 11.6V going to it, is this right? All of my other guages work fine, what am I missing?

[Bob B.]

Sounds like the wire going to the sender is grounded somewhere.

[byrd]

pull the wire off the sending unit and turn on the key and see what it does, I agree it does sound like a dead short in the wiring.

[71see10]

Had one do the same thing today, check to be sure that the resistor on the bottom side is grounded if it not the gauge will go to H !! I put a jumper to the plate that holds the two gauges. hope this helps!!

[bowtieboy93]

u ever think it just might be real hot real fast?........lol

[Hardway]

Even with the wire off it goes H immediately. The instructions say to not use the original resistor on the back since it has one built in, is that the resistor you are talking about 71see10? I do agree, it does sound like a short somewhere but with all new wiring, a new printed circuit board, and gauge I can't figure out where it could be coming from. Any other ideas? If i take the cluster out what voltage should I be getting at the cluster connector?

[El Jay]

I hate electrical probs.
But have you checked the sending unit itself?
I just looked thru a couple of manuals I have & unfortunately, I can't find any info on sending unite.

[VetteVet]

Here is a copy/paste from a great web site.

Water Temp Gauge Trouble Shooting
Electric type temperature gauge system consists of an engine thermal plug electrically
connected with registering gauge mounted on instrument panel. (Refer to applicable
wiring diagram). System is activated when ignition is turned on.

The engine unit is mounted in engine water outlet housing on straight-six & four cylinder engine, or in
engine water manifold on V6 gasoline engines. On diesel engine models, the water temperature indicator is
mounted on the outlet side of the engine front cover. Engine water temperature at these points, acting on
element in thermal plug, causes variation of resistance in electrical circuit.

Testing Electric Type Indicator
1. Disconnect wire at engine sending unit. Ground wire to
engine block. If gauge registers when ignition is turned
on, you may have a bad sending unit, test as follows.
2. Connect a test light consisting of a 12 volt, 2 candlepower
bulb, & a pair of test leads in circuit by clipping one lead
to battery positive termainal & other lead to body of engine
sending unit. If bulb lights, uint is properly grounded. If
bulb dose not light, check for presence of sealing compound
around threads ot unit. Remove compound & repeat test. Make
sure unit is properly ground before proceeding with next test.
3. Remove test lead from body of sending uint & connect lead to
termanal of unit. If bulb lights, engine sending unit is
internally short-circuited & should be replaced.
4. Remove test light & reinstall wire on Sending Unit.
5. If engine sending unit test satisfactory under the above
conditions, check the following items according to nature
of difficulty.
A. If gauge dose not register when ignition is turned on:
This may be caused by a break in the circuit between the
gauge & the ignition switch or a short between this lead
& ground.
B. If gauge shows high temperature under all conditions; wire
leading from gauge & engine sending unit is shorted
to ground. C. If gauge registers a low temperature under all conditions,
wire between gauge & sending unit is broken.


Do Not Attempt to repair either the engine sending unit or the gauge. When installing new engine
sending unit, Do Not use thread compound on sending unit threads, as this will increase
electrical resistance og unit & cause faulty reading on gauge.

[Hardway]

Thank you for the detailed troubleshooting info. I will try to attack this tomorrow or first this over the weekend. I will post my results as soon as I have some.

[Hardway]

If I had hair I would be pulling it out right now. I can not believe this happening with a brand new wiring harness. The sending unit is properly grounded according to the test below and not internally shorted. With the sending unit wire back on I get 1.2v at the 2 threaded pins where the circuit board connects when the key is on. Is there any way to test the gauge itself? I do not have an old gauge to test with. Can someone tell me how to connect the temp gauge directly in to the truck and bypass the original circuit all together?

[Hardway]

Its the GAUGE!!!! I dug through every box I had thinking I might have an old one sitting around and whala I did. I installed with it's original resistor in place, turned the key, the needle drops to C immediately. I am calling LMC tomorrow to get a replacement sent to me. Thank you for all your help guys.

[72 CustomCamper]

At least you figured it out. I've had a few electrical problems in the past that I had to give up one and send the out to be fixed. The sad part was, I was trying to fix them for a friend...


Chuck

[71see10]

Glad to hear that! Sorry I couldn't be more helpful. Brian

[67mater]

I love this site !!!