Hooked up battery backwards!! :-(

[Johnnyboy101]

So... I bought a 325i a few weeks ago. Decided to get a new battery because the PO was using an improper size. Both terminals use black wires... And I hooked it up backwards :-(. I didn't realize my mistake until after I had tried starting the car. Went back and swapped the terminals around. The car starts but now battery light and antilock brake light is on (even when the car is off) There is a burning smell coming from the alternator. I am guessing that is toast. Windows work, lights work, no radio though. I am hoping it is just the alternator and radio... Anything else I should look for???

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[jeffnhiscars]

You blew a diode in the alternator. Not sure about fixing it.

[Johnnyboy101]

Would the car start if I fried the ecu?

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[wilholl]

ABS relay will be dead as well

[RedTeam]

I made the same mistake, but while jump starting my car. It could just be the voltage regulator for the alternator, but you may have to replace the whole unit. I found a replacement alternator for a pretty good price, swapped it, and now the engine runs fine. Radio still doesn't work though, and the corresponding fuse is intact. I've read something about a fuse on the back of the head unit, but there's all sorts of crazy stuff flying around the Internet these days. If anybody knows about this, I'm interested as well.

[modernist]

Would the car start if I fried the ecu?

Nope

alternators are inexpensive and easy to replace, so are ABS relays.

~

some head units do have a fuse in the back. The best way to find out would be to remove the head unit and take a look look.

[Kershaw]

Every aftermarket head unit that I've had has had a 10 amp fuse in the back.

[Johnnyboy101]

Just ordered a reman. Bosch alternator and abs relay. I've also heard mention of some fuse in the trunk called a fusible link? Should I replace that too?

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[bangn]

doubtful you would need to, current was only reversed otherwise that would of saved your alt if it blew.

[Das Delfin]

if your fusible link was blown I don't think the car would start

+1 to a fuse in the back of the radio

[Johnnyboy101]

Just want to say thanks guys so far for all the advice! It is much appreciated! My parts should be in on Monday... once installed I will see what isn't working at that point. Don't want to jinx myself but if all I have to replace is the alternator, the abs relay, and a fuse on the radio, I will consider myself lucky!

[Johnnyboy101]

Good News...

I replaced the alternator today. Pretty straightforward in and out. Only issue I had was getting the belt back on. I will be replacing all 3 accessory belts this week. Good new is no more battery light! Just need to replace the ABS relay and radio fuse and I should be good to go. Glad these cars aren't all electronics like they are now, otherwise I would be in trouble.