I can't quite figure out their color coding.

The 2nd wire from the left looks like it is brown. Is that the ground?

The first one (yellow/green) goes to sendor switch, I ring this out and it was fine. When I check resistance between the 2nd wire and chasis ground, I get OPEN. I believe it is 7th or 8th from the left was ground, don't remember now.

Thanks for taking time to help me out.

According to the picture, which one you think should be ground? If ground is missing, where would I look?

 

Hi,

Can you tell me which one should be ground wire on above connector for the temperature gauge?

I don't to ground something to test?

 

The cluster has two brown wires going to chassis ground.

One ground is just for the temp gauge. It runs to a junction box on passenger side of car then chassis ground.

The other is ground for tach, fuel, and speedo.

White/Black ground the gear indicator bulbs and few other items.

Black wire goes to light rheostat.

 

Some more info

When I unhook the connector from the sender, the gauge reads cold - That means the wire is not grounded. Correct? If this wire was grounded , the gauge should have pegged.

With the connector unhooked I checked resistance to ground and that was 60 ohms, that's low. Isn't it?

I then connected potentiometer (variable resistance between sendor connector and ground. Around 350 ohms the gauage reads about half way, at 650 ohms and beyond gauge reads cold. So the gauge appears to be working fine.

I'm really confused and I'm back to the sender which has been already replaced and reads 650 ohms when engine is cold.

 

Yes confusing.

The less the sender resistance, the higher the gauge temp reading.

Don't know what the connector reading to ground is supposed to be.

Have you checked brown wire continuity with chassis ground?

Suggest taking ohm readings from old sensor at room water temp, 100F and 199F.

Use the pot to simulate this resistances. At room temp should be at bottom, 100F low and 199F midway or slightly below.

Normal operating temp is below 199F. Needle location stays solid typically at slightly below midway on gauge as electric fans kick in to cool radiator at 199F. And normally needs does not get higher.

Make sure you are using a conductive sensor thread sealant. And the sensor ground (coolant plumbing) is same as chassis ground. The engine has a ground strap between engine and chassis. Sensor is grounded at plumbing, gauge at chassis.

 

<<<Brown wire to ground. >>>

In the picture I posted above is that the 2nd wire from left, next the yellow/green sender wire? There are 2-3 wire with similar colors and I can't figure out which one is which.

I didn't use any conductive sealant, I use little Teflon tape.

I hooked up potentiometer to ground where the sender unit is and gauge was working fine. So that tells me wiring and everything else is okay. May be it is sender.

 

Wiring shows two brown (ground) wires for the complete gauge console unit. Both should go to chassis ground. The one for the gauge goes via a junction box to ground.

Make sure the brown wires at their plug terminal have 0 ohms (or close to it) with chassis.

Heat sender in water and get ohm readings up to 212F, then simulate with pot. At 199F setting needle should be in middle or slightly below.

Check the resistance of the pipe the sender screws into to chassis ground, should be 0 ohms (or close to it). Pipe and chassis are return electrical circuit.

 

Some more checking today and I'm convinced now that wiring and everything is alright except grounding. It seems like sender is not grounding to the pipe for some reason.
I don't know if it is problem with the sender or there is problem with the pipe/engine ground.
Since this is 2nd sensor doing exactly the same thing.

 

Ground sensor to a bare chassis point or negative battery terminal and determine what happens..

 

Did you mean leave sensor in it's pocket, take a jumper connector with alligator clips on both ends and attach one end to known good ground such as bare chasis or negative terminal and other end to sensor body?

I pulled the sensor out of its pocket, hooked it up to its connector and jumpered the outside brass body to ground, I did not do it to negative terminal, with new sensor, the gauge was still pegging, I did the same thing with old sensor and that reads cold.

I'm suspecting may be on new sensor there is still coating which is not providing it a good ground reference. I scrapped outside body a little and it was still the same thing, except the gauge would move slowly towards high.


Can you spary or how do you clean inside of pipe threads where sensor is really touching to the ground. I don't want to screw up threads. Unless there will be no problem with threads, once the engine is properly grounded.

I don't know if coolant has coated the inside surface so it's not conducting well.