Temp Gauge Troubleshooting

I am sure this has been covered somewhere on the internet in exacting detail, but after a healthy amount of searching and reading I am left without an answer and curious as to the thoughts of others…

My original goal was to get the temperature gauge working again on my ‘71 CJ5. Engine has been rebuilt and there’s a new sender and wiring, but the gauge is original and I’ve never seen it move off of C. The fuel gauge sorta works. Here be the facts:

1. I removed the new sender and tested on the bench for resistance. Came back in the 250 ohms range (feels low) completely cold.
2. I reinstalled it and tested again without the wire connected (again cold). 400 ohms range. (Feels right)
3. I reconnected the wire. 16.5 ohms regardless of temperature. Obviously way too low.
4. Tested the resistance between the posts in the gauge and got 6.5 ohms. I’ve read that this should be closer to 20 and also that a blown gauge will read zero.
5. Pretty sure there is power to the gauge as the fuel gauge works and wiring is there. Long story but I blew my multimeter like an idiot before I tested voltage, so tbd. FWIW, the fuel gauge works but reads just above half at what I know to be full. Haven’t gotten down to empty so I don’t know where it bottoms out.

Is this obvious to anyone?

Anyway, I ordered a new temp sender because they’re relatively cheap, but I sorta suspect it’s my gauge that’s the problem. I really want to avoid replacing because it’s original. Any thoughts before I do that are super appreciated.

 

Can't put my finger on it right now but search some more. There should be lots of post here on the subject. I can say your ohm readings sound a good bit off. Do you have a TSM? Could be a problem with the voltage regulator in your fuel gauge. Plan carefully before testing with a volt meter, make absolutely sure the gauges and are well grounded to the custer case (inside the cluster case) and the cluster is grounded to the dash or the neg battery post. Make sure you have a though understanding of how the system works before you test to prevent frying your gauges, VR, sending units.

 

x100

 

Not meaning to send you to another forum, but Jeepforum.com has a member, John Strenk, who is an absolute wizard when it comes to troubleshooting gauge issues. You might want to either do a search there or ask him yourself.

 

Thanks for the advice - I’ll check the grounding and also check out John’s posts.

Unfortunately I don’t have a TSM, but I think I found the right resistance ranges online.

 

And we know anything on-line must be true. Get a FSM.