Gauge Cluster Issues

[Skippy]

While troubleshooting a different problem, I had my gauge cluster out and apart. I've put it back together wrong, apparently. New issues: Gauge lights don't work. Fuel gauge pegs at full on startup, and temp gauge goes to full within a minute or two of starting. High beam indicator stays on. Other info: The rheostat has a jumper soldered across it. There is also a jumper from the rheostat to the #3 pin on the round electrical connector to work around a bit of the PCB that flaked off years ago. I originally installed it years ago, and it came off as I was pulling the cluster. I got Pin 3 based off a post I saw on this site, but I'm not sure that's correct.

What did I do wrong?

Edit: The patient is the '83 300D in my signature.

[H-townbenzoboy]

You may have put the 15 pin plug in wrong and shorted some stuff. It's a keyed plug, but it does happen. Or your ground might be wonky now after this last cluster R&R and may need a new ground cable from the cluster to the ground behind the dash.

[Skippy]

I'd consider having the keyed connector in wrong unlikely. However, the ground thing sounds quite plausible. What are some good places to connect an auxiliary ground?

[vwnate1]

Use an part of the body, use a star typ lock washer under the nut and ring lead .

German cars use brown wire for grounds .

[Skippy]

Originally Posted by vwnate1

Use an part of the body, use a star typ lock washer under the nut and ring lead .

German cars use brown wire for grounds .

Where on the cluster?

[Felching]

Any screw on the speedometer.

[Skippy]

Originally Posted by Felching

Any screw on the speedometer.

It seems to have worked. The fuel gauge is now reading a plausible value instead of pegging full. I'd take it for a test drive, but I'm going to walk over and grab a pambazo first. It will be a few hours before it's dark enough to tell if I fixed the dash lights. I may work on the Jag a little bit.

[MS Fowler]

I have seen where the keyed part of the plug had broken off making it very easy to misalign the connector.

[dieselbenz1]

Originally Posted by MS Fowler

I have seen where the keyed part of the plug had broken off making it very easy to misalign the connector.

X2

[Skippy]

The D-shaped key was still there when I had it apart last, and I didn't have to use much force to get it in. We'll see when I take it apart this weekend. I do wonder how a ground issue could result in the high beam indicator being on, albeit too dimly to see it during the day.

[steeleygreg]

One way to test out the cluster ground circuit is to use a long test cable. Connect one end to the battery grnd point the other end would go to the grnd point on the wiring harness. Using a continuity meter will verify the wiring harness grnd point to the cluster. If the key "D" shaped connector is still connected to the plug then I can't see how this would cause a problem.
MB's have a funky issue with with grnd circuits. In electricity devices will seek the least resistant path to ground and can take out other circuits in the process.
Please don't ask how I know this......

[optimusprime]

Any good .W123 diesel

[vwnate1]

" I do wonder how a ground issue could result in the high beam indicator being on, albeit too dimly to see it during the day."

It glows because the indicator lamp is providing a poor ground path .

Like the millions of old 50's & 60' GM products that have a dim taillight that goes out when you step on the brake : the secondary filament provides a ground path until you energize that circuit then the light goes out .

Auto electrics isn't rocket science, you just need to learn it by doing, you'll get this fixed ere long .

[Skippy]

I'll try that.

[vwnate1]

I'd take a photo and post it if it wasn't so god damned difficult to do so, it used to be simple, now it's almost impossible to upload any attachments .