1980 Dasher Temp gauge not working

[frankclimbs]

So I just acquired a 1980 Dasher with a 1.5L Diesel engine. It was my grandpa’s car and sat for almost 20 years. I now have it running but I can’t seem to figure out why the temperature gauge is not working. Looking through the forum I couldn’t find a solution. I located the temp sender and the wire attached is a yellow/red which seems to be correct. In one of the posts that I read it said there should be 10 volts to this wire when the key is on. Can anyone confirm this? Mine does not have any voltage. I am guessing this is my problem. I assumed that the wire was probably cracked somewhere and not getting the voltage it needed. But I did a continuity test and it appears to be good from the dash to the sender. So my question now would be what to try next? My fuel gauge works great as just some more information as many link the two. Is there a fuse or relay that I am missing? Any help that anyone can provide would be much appreciated. I am excited to get this car back up and running on the road.

I plan on posting some progress pictures along the way as I restore this car. Thanks again.

[vwoldbug]

Are there more than one sending units . Do you have a repair manual with a wiring diagram to make sure that's the correct sender . I believe there is a sender for the glow plugs . If that's the correct sender have someone watch the gauge with the key on engine off and touch the wire to a good ground and the gauge should move . Good luck

[frankclimbs]

Thanks vwoldbug. You are correct that there are two senders and one is for the glow plugs. I identified that one and it does work. If I remove the wire from the glow plug sender the light just stays on. It is blue/white. Which is a little weird as I do have the Bentley repair manual and I believe it should be blue/yellow.
I will have my wife help me out later today to see if I can get it to move. I guess the other thing I can try is to swap the two wires to validate that the sender is not bad. Thanks again for your help.

[vwoldbug]

Switching the wires should help . I think you can check the senders with an ohm meter.

[kamzcab86]

[vwoldbug]

If you have the cluster out check circuit board for a break. If this turns out to be no parts available you can always install an aftermarket vdo temperature gauge and oil oil pressure gauge . They aren't too expensive .

[frankclimbs]

Thanks for the suggestions. I have not yet pulled the cluster. If I can't get it to move, that will be my next step. I will let you know when I test it tonight.

[frankclimbs]

So I swapped the two wire and still no temp gauge. So I then had my wife watch as I grounded that cable out as well. The gauge didn't move. So my project now is to pull the instrument cluster out and take a look behind there.

Is there any special I should look for or tests that I can perform on the gauge itself?

I am hoping I might get to this tomorrow but it might be put on the back burning until early next week as I am planning on replacing my timing belt and accessory belts tomorrow. I figure after sitting for 20 years these belts are do for replacement even though they look great.

[sgnimj96]

I put a regular gauge sensor where the uselss a/c cutout switch was, if yours had a/c.
https://volkswagenownersclub.com/vw/showthread.php/28183-Thermal-Switch

[Dampcamper]

I am resurrecting a new-to-me 81 Caddy Diesel and had to do a fair amount of work on the instrument cluster. The fuel gauge and temperature gauge get their power from a little 3-terminal regulator (looks like a small power transistor) that makes a steady 10 volts so the gauges don't wander as your DC + battery voltage fluctuates. The gauges in my cluster had little nuts holding the flexible circuit board to the gauge supply and sense screw posts. There was no power getting to either gauge. I have some experience soldering in weird situations and so was able to create some bare copper on the traces before they got to the gauges and get a droplet of solder to adhere; then used very small wire (like 24 gauge) to connect to that and a lug to go under those nuts.
These flex circuit boards are tricky to solder to. Don't use a gun! I used a temperature-controlled iron at 700 degrees and had to work fast, even then burned a hole in one place (I had several failed connections on this thing). I just put it (the cluster) back in or I would send a picture, sorry. But use smallish flexible wire for these jumpers so they don't stress the flex board foils, if you use big wire it will likely break the traces when flexed. They are not really robust.
Of course if your fuel gauge is working (fed from same regulator on my rig, is it with yours?) you could carefully run a little jumper wire from one gauge's supply post to the other. Just be really careful unscrewing that nut so you don't twist and break the good foil connection.