Temperature gauge not working

1972 B-Body with standard gauge cluster.

My temperature gauge decided to quit work. The needle stays to the left at cold no matter how warm the engine gets.

I replaced the temp sensor. I also inspected the board at the back of the gauge pod and there was no visible defects. My engine harness is a replacement from Year One and is in excellent condition.

Are the gauges themselves known to go bad? I noticed the light bulb on that end of the cluster doesn't come on with the headlights. I haven't pulled the bulb yet to see if it's burn't out. Likely just a coincidence and not related.

Are the rest of the gauges working?

yes it can go bad, be burned out.
not usually an issue but you can test it by wiring 2 AA batteries in series and touching the leads to the posts on the gauge. it should move to half way.

if your fuel gauge works, you can eliminate the voltage reg from being the issue, but if it doesn't work then that would be my first go to.

the bulb near it going out could be nothing, or ground on that side of the cluster could have an issue. that too might take out the gauge if ground isn't making contact.

any changes done recently?

Yes. The fuel gauge and amp meter are working.

I just swapped intakes, but it wasn't working previous to the swap. I installed a new sending unit in the new intake and it still doesn't work.

so you could have pinched the line so even if it looks good it could be broken internally.

you can ground the line in the engine compartment and then turn the key on and see if the gauge moves.

then if it doesn't try grouding from the bulkhead connector and test again.

IF it doesn't work from the bulkhead and you are sure you grounded it, then maybe the gauge died.

if it is possible you pinched the line grounding out the line causing the gauge to peg and you didn't notice, you might have burned it out.

Not wrapping the threads of that sending unit in teflon tape and/or sealer are you?...

It was working when I pulled the car out of storage a couple of months ago. It's stopped working before I did the intake swap so there was no changes made prior to it not operating. Thus this is unlikely.

Yes I used teflon tape.

This is the proper way to troubleshoot the gauges. All I can add is that I too have had trouble with Teflon tape but not with thread compound. An easy check is to measure the resistance from the sender body to the pump housing. Should be zero.

NO tape or sealer on the threads, as this is your ground, this may be your issue or part of it...

Maybe, it's definitely easy to test. I'll try grounding out the lead to the sensor tonight and see if it pegs the gauge.

Don't let it peg the gauge just turn the key on long enough to be sure the needle rises over half way. Pegging the gauge will burn it out.

1. I grounded the sensor connector directly to the battery, turned the key on, and the temp gauge didn't move.

2. I pulled the bulkhead connector at the firewall and verified there is continuity.

3. I checked resistance at the sensor and it's at 0.2 ohm, so the sensor is grounded.

4. I inspected the bulkhead connector and reinstalled it. With the sensor connector still grounded I turned the ignition on hoping the bulkhead connector was maybe loose previously. No dice.

It looks like my problem is inside the firewall.

Did you ground the sender wire or the sender itself. You need to ground the wire not the sender.

I grounded the connector and checked resistance across the sensor. Everything under the hood checks out.

I see why you questioned it so I fixed it.

so if you can reach the connectors under the dash, see if you can connect aligator clips to each of the posts.

then you can wire up the batteries to it and see if it moves or use a test light to check for a pulse.

if you can't reach up to it, then you have to pull the cluster to start running tests.

oh you could verify blinking lights at the sensor too with a test light.

I hooked batteries up to the posts on the back of the cluster and the gauge moved, so the gauge itself is good. So the problem is between the gauge and the firewall.

I wouldn't assume you were getting voltage from the IVR to the gauge unless you verified that. Amp gauge doesn't use it, the fuel gauge does, but you can still have a crack on the board that feeds the gauge. BTDT.

When I have time I'll remove the radio so I can get at the main connector for the dash so I can inspect the pin for the temp gauge and check continuity to the sensor connector.

I wouldn't be surprised if there is a problem with the board on the back of the cluster. I replaced the board about 3 years ago when I had the column out for the power steering conversion. I replaced it because the connection to the right turn signal indicator was broken.

If I have to replace the board again this time is will be a brand new one.
https://www.ebay.com/itm/Mopar-Standard-Dash-Cluster-CIRCUIT-BOARD-71-74-B-Body-NEW-PDD-051/332494993093?hash=item4d6a3ef6c5%3Ag%3A4rIAAOSwyYFaO-Dg%3Asc%3AUSPSPriority%2154911%21US%21-1&_sacat=0&_nkw=mopar+b+body+gauge+cluster&_from=R40&rt=nc&_trksid=p2334524.m570.l1312.R2.TR0.TRC0.A0.H0.Xmopar+b+body+g.TRS2&LH_TitleDesc=0%7C0

check with a test light at the sensor and bulkhead and the gauge. you can start with the gauge and work your way forward to find the break.

it should blink.

The fuel gauge works, so the voltage regulator is good. Since I did have to replace the circuit board once for another problem there's a high probably that's where it is.

My plan is to remove the radio to get to the main cluster connector then check continuity from the dash to the sensor. If that's good there is a problem in the circuit board. If not, then I'll check continuity from the bulkhead to the to the dash.

if you were able to reach up to test with a battery that the gauge moved, then it would be a quick check to see if the pos post flashes.
that will let you know if it is teh circuit board or wiring from the dash to the sensor.
no flash, board, flashing means wiring trace.

Just because the fuel gauge works does NOT mean the one of the traces to the temperature gauge doesn't have a crack in it, either from the IVR or from the pin that eventually goes to the sender.

you did check the wire at the sender with a multimeter to see if it had a jumping 5 volts ? or did i miss that ?

It's been hot and humid for the last week so it's hard to spend much time in the garage. I'll bet the radio removed this morning before it gets too hot out so I can check continuity from the cluster connector to the sensor connector. If that's good then the problem must be in the board.

I haven't had time to perform anymore diagnostics, but I drove the car last night and now my left turn signal indicator isn't working. So the whole left end; temp gauge, indicator, and dash light is dead. This means there's a good chance that there is a problem with the circuit board.

Sorta curious about this statement. So without any kind of sealant on the threads of sending units ( be it water, oil, or such), how do these things not leak?

I believe they are tapered thread. Factory never used sealer so there should be no reason to now.

Just me for permanent out the door work I use a slight bit of sealer on the top half of the threads (just my OCD) then ohm the body to the nearby block to confirm continuity but I have swapped senders/1/8 NPT mini pipes/fittings when doing gauge setup/psi checking/drill priming & no leaks.

https://en.wikipedia.org/wiki/National_pipe_thread

see NPTF specifically

Yes, NPT is tapered thread that in theory should be self sealing. However, since I was installing the sensor into a 48 year old cast iron intake I figured I'd rather be safe than sorry and used a thread sealer. After 48 years the threads in the intake are likely worn and/or pitted.