Nonfunctional Temp guage............stumped

[boneheaddoctor]

Was all over skinnerbox.steaky.org and can't find wiring diagrams for the temp guage circuit.....I opened and shorted the wiring at the temp sending unit guage never moved.....bought another guage.....still doesn't work....need to trace the wiring out and can't find a wiring diagram to find possible points of failure.


Any ideas?

[tangofox007]

Originally Posted by boneheaddoctor

Any ideas?

No idea....which model you are referring to.

Does the car have a Tobacco interior? Or Palamino?

[boneheaddoctor]

Yeah...your right I forgot to mention that.....


its My 1983 300D W123

[tangofox007]

I have the electrical diagram for the '82 300D. (The '83 could be different.)
It shows that the coolant temp gauge is powered through terminal #6 (blue/red wire) on the instrument cluster round plug. It is grounded through terminal #2 (green wire, running to a connector on the left front fender well, then to the coolant temp sender.)

Correction: The coolant temp gauge is powered through terminal #6 (black/blue wire.)

[boneheaddoctor]

Thanks....I'll check this out tomorrow morning.....this guage not working is irritating me to no end.

[Palangi]

When the temp gauge quit on my 300D I found that the junction where the terminal is crimped on the wire at the sensor had corroded. This would be inside the little plastic insulator thingy. Fixed by a little soldering work. The little plastic insulator is available separately and the dealer had it in stock. The root of the problem was that the sensor was not screwed in tightly enough. It was letting trace amounts of coolant out which was wicking up the wire and causing the corrosion.

[boneheaddoctor]

Originally Posted by Palangi

When the temp gauge quit on my 300D I found that the junction where the terminal is crimped on the wire at the sensor had corroded. This would be inside the little plastic insulator thingy. Fixed by a little soldering work. The little plastic insulator is available separately and the dealer had it in stock. The root of the problem was that the sensor was not screwed in tightly enough. It was letting trace amounts of coolant out which was wicking up the wire and causing the corrosion.

Will look at that first.............as its quick to check.....thanks.

[Johnhef]

also make sure if there is more than one place to plug the sensor, thats its plugged in on the right contact, I've had them switched before and got a dead gauge.

[boneheaddoctor]

Between pin#2 of the cluster plug and the plug at the temp sensor on the thermostate housing I get 819 ohms resistance..........this is not right.......

[tangofox007]

Wrong temp sensor!!! The coolant temp sender is on the left side of the engine, opposite the IP. (Between #2 & #3 glow plug.)
The sensor on the thermostat housing is the "cold engine lockout switch." It prevents the ACC from running the blower when heat is selected, but not available.

[boneheaddoctor]

Originally Posted by tangofox007

Wrong temp sensor!!! The coolant temp sender is on the left side of the engine, opposite the IP. (Between #2 & #3 glow plug.)
The sensor on the thermostat housing is the "cold engine lockout switch." It prevents the ACC from running the blower when heat is selected, but not available.

Yeah....I figured that out...the hard way. Becasue it only has two temp sensors and that one had the wrong color code....the one behind the IP did have the green wire on it.

I have continuity from that connector to #2 on the plug.....but no movement from the guage.., when either open or shorted....to determine if the sending unit is histor or not.........damn this is frustrating.

Two guages have done the same exact thing......

[boneheaddoctor]

Any ideas why all the other guages are working fine but the temp guage isn't moving at all?

And this is two different guage assemblies that do this.

[tangofox007]

I would wire the original gauge (assuming that it is not currently installed) from the battery to the sending unit. If the gauge works, the problem is most likely a broken trace on the instrument cluster board. If the gauge does not react when you ground the sending unit connector, the sending unit is not likely the problem.

[Wes Bender]

Originally Posted by tangofox007

I have the electrical diagram for the '82 300D. (The '83 could be different.)
It shows that the coolant temp gauge is powered through terminal #6 (blue/red wire) on the instrument cluster round plug. It is grounded through terminal #2 (green wire, running to a connector on the left front fender well, then to the coolant temp sender.)

Tangofox, my schematic shows that the temp gauge gets power from pin#5 rather than pin #6 of the round connector. Pin #6 is the "balance" voltage for the Charge Indicator light.

BHD - I would think it unlikely that you got two bad temp gauges and would suspect something else. Check to see that you are getting 12 volts to the indicator with the key on. Sounds as if the sender is OK, although you should check resistance through the sender, hot vs. cold, to see if it is working. I'll see if I can find some resistance values for you.

Wes

[boneheaddoctor]

Originally Posted by tangofox007

I would wire the original gauge (assuming that it is not currently installed) from the battery to the sending unit. If the gauge works, the problem is most likely a broken trace on the instrument cluster board. If the gauge does not react when you ground the sending unit connector, the sending unit is not likely the problem.

No the original guage is on my desk the replacement is in the dash right now....

I will see if I can find some jumpers I can clip to +12 and ground to make the guage happy...
I assume power is on pin #5 as fuel guage works.


I realized I had the Haynes manual for a W123 that actually was in my W116 when I bought it.....so I found the wiring diagrams there.....totally forgot I had this book.