I was looking for an AC main switch on eBay and this popped up in my search. I don't know anything about it but I thought I would post it in case this means something for someone with an E3...
https://www.ebay.com/itm/BMW-E3-280...m=132821623793&_trksid=p2047675.c100012.m1985
https://www.ebay.com/itm/BMW-E3-280...m=132821623793&_trksid=p2047675.c100012.m1985