I smoked the instrument cluster in my 420sel a bunch of times. I took the cluster out to replace some bulbs and when I put it back in I got smoking and gauges going crazy. David S Poole told me to ground the cluster with alligator clips or similar and that cleared up the craziness of the cluster. AS for the smoking I think it did some permanent damage to the car. While my gauges and blinkers and headlights worked properly , all the idiot lights quit working on the right side of the steering wheel except for the SRS. The oil level light came on all the time and would go out whenever it wanted. I tried swapping clusters and it still had the same problem. As for the huge plug in the back, I also broke the little plastic tab, but I could still tell where the pins were supposed to go. I still got em wrong occasionally and smoked up my IC.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual