Thanks. My friend learned quickly that there were no suppliers for ref pots, so he pulled a spare out of an old ETA and soldered it in. For troubleshooting purposes, he was getting an open (no voltage) when he tried to run voltage through the original ref pot at any setting.

I guess a replacement can be done, but you have to be lucky in addition to having good soldering skills. I was impressed. Hope it never happens to me.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles