Firstfives.org

Saw an AD for a 76 530i. Owner claims the car won't start because "battery chartered reverse polarity"?...I'm assuming this means the battery was hooked up wrong? He took it to a mechanic who installed a new fuel pump and confirmed it was working thru the relay. He replaced the ECU and the alternator but still no go so assumes it is a wiring issue? I guess his mechanic was stumped but that's not surprising since there aren't a lot of mechanics around that are familiar with these cars. Just curious as to what you would do next to track down the problem

No good answer, I'm still thinking, not ignoring you.

Start with the basics, does it have spark? It should, but never assume. If you're thinking of replacing your car with it, you would always have the harness from yours, which is very much a separate harness except for a few wires that meet at the combo relay. It was a 76 harness I used on my '69 Bavaria when I put FI on it and really there wasn't a whole lot of wiring I had to do.

The car is in another province so I don't have access to it. It's a well preserved one family owned car in great condition and mint interior. The Ad says he wants $5000 for it but if it's not running I can't see him getting it. He must have sunk a fair bit of money into it to take it to a shop and have the fuel pump, ECU and alternator replaced? He must have decide to sell when it was a no go after that. I wonder if when he hooked up the Pos and Neg battery posts wrong that would destroy the Combo relay and other all the electronic components and that's why he has a no start?

There aren't really many electronic components in it, the combo relay, ECU and alternator are the only ones that come to mind.

I think your right. Seeing as how he already replaced the ECU and the alternator and the fuel pump is working I bet the car would fire right up if he replaced the Combo relay. Seems like his mechanic is not familiar with E12's!