Aftermarket temp gauge stopped working

[Cody]

Anyone recognize this gauge? It's in a 1980 Cj7 with a sb350. I think it's a sunpro, but I can't find anything on the internet that matches it.

It has a heavy black wire that goes to a sensor on the manifold, and then a thin red wire going to a center post and a black wire going to ring terminal. The black wire is not connected to anything (same with oil pressure, and that gauge works). The red wire shows continuity to ground.


This was working until just recently and has stopped. It's mechanical, so I'm assuming the little wires are for dash lights. Is the gauge bad? The sensor?

I also have this weird connector that I can't figure out an origin story for, but also shows ground.

 

[Hickey]

Did the gauge light up with the dash lights previously? I’m wondering if it’s the sensor/sending unit itself.

 

[Cody]

I believe it did. When it's dark I'll investigate the dash lights

 

[I Lean]

If it has a wire going to a sensor on the engine, then it's not "mechanical", it's electrical. And the sensor will just show different resistance at different temperatures, so it will probably always show continuity to ground.

Anyway, my bet is you have an open circuit. I'd start by grounding the black ring terminal just because that seems like an obvious suspect spot.

I bet you could also find a wiring diagram for a similar gauge somewhere. It's likely a "signal" wire from the sensor to the gauge, a hot-with-lights wire for illumination, and a ground wire. And maybe a switched hot also? Not sure.

 

[Cody]

This is the connection to the block. Top left

 

[Cody]

There's actually another wire on the top of the gauge that heads into the dash. That might be the dash lights?

I did ground the wire coming from the ring terminal and it didn't change anything. I wonder if that's actually 12v? Just seems odd that a red wire would show ground.
.. And the black is disconnected on the oil gauge and it seems to work

 

[I Lean]

There's actually another wire on the top of the gauge that heads into the dash. That might be the dash lights?

I did ground the wire coming from the ring terminal and it didn't change anything. I wonder if that's actually 12v? Just seems odd that a red wire would show ground.
.. And the black is disconnected on the oil gauge and it seems to work

The oil guage looks purely mechanical though, right? Meaning, a tube with oil going to the gauge itself.

 

[Cody]

Well, there is a tube of sorts there. I haven't investigated the guts but that sounds plausible. The red and black wires coming off the oil and temp are set up the same way..in fact the red wires come together before heading to ground and the black wires are stripped but don't go to anything. I'm wondering if the black wires went to the male side of that weird female connector (looks like a tiny antenna connector) and the connector fell off. But if that's the case, why would both wires off the back of those gauges be ground?

I can find a diagram for a different sunpro gauge ending in 32. It definitely matches the example of the mechanical schematic, but the wiring coming off is different.

 

[shortstraw8]

Did the sensor die? Do you get any resistance with a meter when the motor heats up from the sensor itself?

The other red wire with should attach to the back on one of the sensors for lights?? I can't remember but looks really familiar when I had to swap the oil pressure gauge on my cj. That tube does carry oil, so don't forget to hook it up on both sides right or you cover everything in oil. Forgot the motor side and had an unexpected oil change and oil covered driveway.

 

[Cody]

How do I test the sensor? I idled in the driveway for about 15 minutes. The fans kicked on.... I think the kick at 160-170? But the temp just barely moved off of the bottom pin (130*)

 

[shortstraw8]

If you have a meter with ohms you can disconnect the wire and touch the probe to the center terminal and touch the other probe to the body of the sensor and see ohms grow as it heats up.

 

[Cody]

OK so the dash lights work how it's wired now.

 

[OldGeezer]

The red wire is the dash light, the thin black wire is probably a ground that is not used because your gauge is grounded through the metal dash. The heavy black wire is for the sensor. It should unplug from the sensor on the block. Mine gets soaked in oil and I have to clean the terminal every once in a while. Yours looks to be dry. The red wire shows ground because a bulb filament doesn't have much resistance.

 

[TurboMinivan]

Test the gauge itself by unplugging the heavy wire from the sensor and touching it directly to the block (or some other good ground source). Does the needle move? (It should go all the way to max.) If yes, the temp sensor probably is defective. If not, the gauge is likely to blame.

 

[lhracing]

It's a mechanical gauge, the "black wire" is a capillary tube, not a sending unit.

The red wire is for dash lights only and does not affect the gauge itself.

 

[85CUCVKRAWLER]

It's a mechanical gauge, the "black wire" is a capillary tube, not a sending unit.

The red wire is for dash lights only and does not affect the gauge itself.

Yes, that gauge is 100% a mechanical gauge. But the black wire in the block isnt a capillary tube, its a thermistor wire. The gauge works without power wired to it as its all based off the thermistor.

I had one in my K5 and the one installed on my LS in the K5. They are very simple but do go bad regularly. The red wire is to light up the gauge when the lights are on. If the gauge no longer reads a temperature, just replace it.

A quick search for the numbers on the gauage gave me this: Sunpro retro temp guage

Vintage Sunpro Temperature Temp Gauge C700-110-30 Mounting Bracket & clamp 2” | eBay

UNTESTED, SOLD AS IS. GM General Motors. 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 second 2nd generation. F Body F-Body Chevy Chevrolet Pontiac Camaro Iroc Iroc-z z28 RS Firebird Formula Trans Am TA T/A.

www.ebay.com

 

[lhracing]

The "black wire" from the gauge to the engine is actually a capillary tube.

This is from one of Autometer's mechanical gauges.

"AutoMeter’s advanced bourdon tube meter movement provides unparalleled performance in the most demanding applications. A 6’ capillary tube and 1/2” NPT mounting nut are included."

 

[Hickey]

I woulda guessed falopian tube, but I ain’t no mechanic.

 

[85CUCVKRAWLER]

The "black wire" from the gauge to the engine is actually a capillary tube.

This is from one of Autometer's mechanical gauges.

"AutoMeter’s advanced bourdon tube meter movement provides unparalleled performance in the most demanding applications. A 6’ capillary tube and 1/2” NPT mounting nut are included."

Capillary tube is for transmitting pressure, such as in a mechanical oil pressure gauge.

Thermistor wire is used on mechanical temp gauges. Because there is no pressure it transmit.

 

[lhracing]

Capillary tube is for transmitting pressure, such as in a mechanical oil pressure gauge.

Thermistor wire is used on mechanical temp gauges. Because there is no pressure it transmit.

I guess Autometer is wrong???