1981 240D electrical gremlins

[koooop]

Maybe this is a known issue, maybe not.

1981 240D, manual.

When I turn on the headlights the gas gauge sharply pegs to full, the temp gauge pegs out, both of the dash turn signals light up, the high beam indicator lights up. The turn signals do this as well snd when I put the car in reverse. None of this happens if I put on the left side marker right light the right side marker, turn on AC, blower or interior lights.

I had a bad headlight switch replaced a few years ago, it was doing bizarre things. I’m Almost thinking this may be related. To that switch.

Thanks

[Sugar Bear]

Sounds like a bad ground connection. Clean and tighten every ground wire (brown) connection you can find, particularly any near the instrument cluster, under the hood near the batt - connection and at the headlamps.

Good luck!!!

[koooop]

Originally Posted by Sugar Bear

Sounds like a bad ground connection. Clean and tighten every ground wire (brown) connection you can find, particularly any near the instrument cluster, under the hood near the batt - connection and at the headlamps.

Good luck!!!

Thanks for the possibility.

So pull out the cluster and start in there maybe?

[Sugar Bear]

Unless the cluster has been removed in recent times, I'd try looking all around/under it to see if removal is necessary to access ground connections. Taking old pieces apart often breaks small things so if removal isn't necessary then don't. If necessary be gentle with it and do it on a warm day, plastic gets brittle in cold weather.

Good luck!!!

[Chilkat]

Mine did similar things and as mentioned, it was the ground. I did what Sugar said and it fixed it, just went through all of the grounds I could find and cleaned them up. Took a little tinkering but it wasn't hard. I think I started at the battery and worked my way in but if you recently did the switch I might start there.

[koooop]

Since I purchased the car 4 years ago it’s had the cluster out to replace the dash light bulbs and it came out easy, a battery and an alternator. I’ll start at the battery and alternator.

The dash lights have gone a little wonky since I bought the car, but it was only over 65mph or if I was winding the snot out of it.

[koooop]

The Benz mechanic spent five minutes, narrowed it down to the dimmer switch for the dash lights in the cluster. He says he doesn’t do those kind of repairs so he just disconnected the dimmer switch and all is good now.

I’ll need to put in a new dimmer switch, this is a teenagers car and the dash needs to be visible at night.

I’m pretty sure that dimmer switch was bad when I first bought this car, I think the prior technician replaced it with one that had been jumped. Too bad he’s dead!

[Alec300SD]

For the time being, just jumper the wires going to the rheostat and the dash lights should be on full brightness.
I used a test lead with alligator clips to bypass a dead dimmer switch on 'Stormcloud'.

[koooop]

So I thought I’d report back since the issue has been repaired.

I went to the dealership that sold me the car, they sent me to a local electrician. He fixed it, he doesn’t speak English so I have no idea what he did... $160.

I never knew the dash lights could be this bright, I think he may have put LEDs in since I had a modified rheostat and the LED bulbs sitting on the seat for him! There were a number of little electrical gremlins in the car, they’re all gone.