I think the tire thing is something to do with ours being a non-limited slip differential. When I got stuck in the snow, I only had one side spinning as well. Also, I don't know what you've done to search for your electrical problems but have you checked your battery to chassis and chassis to engine grounds, plus your voltage regulator? I ask because those gave me really crazy electrical problems on two different occasions, weird lights and wacky gauges and such.

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Seth

1984 300D 225K
1985 300D Donor body
1985 300D Turbo 165K. Totaled. Donor Engine. It runs!!!
1980 300SD 311K My New Baby.
1979 BMW 633csi 62K+++? Dead odo