This may not make a bit of difference in your case but check all of your grounds. Find out where your engine grounds to the chasis and make sure its intact and corrosion free. I had a really odd electrical issue where my gauges where jumpy then all of a sudden it wouldnt' start. I pulled my instrument cluster and repacled it and had the same problem. I noticed every light in the cluster would turn on when the cluster touched the speedo cable. I was getting a steady 2.97 volts from the cable??? I also got random voltages from engine parts that definately shouldn't have had power. Thanks to Craig for telling me to check my engine grounds. I was in a hurry because I'm out of town on vacation right now so I took a jumper cable, attached one end to the EGR and the other end to the negative post of the battery and it started! Unfortunately I had to leave right after that so when I get back I'm going to find my main engine-chasis ground and clean it. It may not help but its worth a shot.

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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