Bmw 5 series will not run

Check connection to the starter? Try it in neutral? Is there an alarm installed? Maybe active but on silent

The ECM is not the only module in the system, you burnt out something that is for sure. In a case like this I suggest you find a really good MB technician, this will be costly.

Yes, you may have put the wires on the starter wrong. There is a positive post and an ignition post. If they touch or one is touching ground then the starter will engage.

easy, if it takes you longer than 7 minutes somethings wrong, and most of that time should be looking for tools.
hidden screw behind handle. 3 wires to unhook, courtesy light down below, master control switch plug, and speaker. step 1 unscrew hidden screw, 2) pop all the plastic keepers. 3) twist the handle through the opening without breaking the connection, 4 unhook 3 wires. bingo it's off.

there is a resistor that needs replacing. It's located inside the car, under the dashboard, near the steering column. If you don't replace, it could run your battery down, as the fan/blower will operate when the car is left.

The battery cables need cleaned even where the termanals connect to the cable and scrape the posts too. let me know. The Raz

What do you mean by that the fan or what

Have a technician check out the battery, cables, alternator,wires behind alternator and the harness they lead to. Further more, have the technician check the entire radio and a/c circuit for shorts and opens.

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new altenator,sounds like you put the cables on the wrong way round