86 190E 2.3 - Tach, clock affected by fastening seat belt

[DieselGuy]

Hello Everyone,

My sister just bought an 86 190e 2.3L. It was previously my aunts car who drove it very little and was always garaged. It has 77,000 miles on it. It's in prestine condition.

Anyway, it does have a couple of electrical issues.

Instrument cluster:
1. The clock works when the ignition is off. With the ignition on, it also works but as soon as you fasten the driver seat belt the clock stops working.

2. The tach works with the engine running. Like the clock, when the driver seat belt is fastened, it stops working as well.

The clock and tach are related I'm sure. I don't understand how fastening the seat belt affects it. When you release the seat belt, the Tach and clock come alive again.

I checked and replaced the fuses for the instrument cluster. I also checked the power feed for the clock behind the cluster. it gets 12.6V with the key off, on as well as the seat belt fastened or unfastened. I suspect perhaps a relay somewhere that supplies ground is faulty.

Another observation was that the seat belt reminder light didn't work. I thought it was the bulb so I replaced it. Still didn't work. This also may be related.

Driver power seat:

3. The driver power seat (w/memory) only moves forward and back, and the rear height adjustment works as well. the back rest, head rest, and front height adjustment do not work. When it move the buttons, you can hear clicking under the seat. The passenger seat has a similar condition.

I looked in the auxiliary fuse box and found a blue 25A fuse blown. I replaced it and the passenger seat became fully functional. The driver seat back rest is fully functional, but the head rest adjustment and front height adjustment going down continually blow the fuse. It doesn't blow when adjusting the front height up; only when going down. The head rest blows the fuse up or down.

I suspect maybe it's a bad control module under the driver seat or maybe the diode everyone talks about.

Maybe all 3 problems are related somehow. Any help would appreciated.

TIA,

Nolan