I messed up. I tried to jump start with reversed polarity.

[claytonH14]

So I'm an idiot. Lets not argue that. But because of my idiocy, my 325is no longer will start. I get nearly every single light on my dash on, but none on the check panel. Is it my ecu? I've checked all the fuses and even the fusible link on the positive lead and none were busted. I've looked at every thread I could find but none gave an exact answer.

Before I tried jump starting, my car would try to turn over and it would move but it just didn't have enough juice because I left my lights on while I was at work. So I got a coworker to help me jump it. I should have known that the sparks were a problem but I didn't pay attention because I was rushing to get to an exam. So, when I tried to start it, nothing. Today, I took the battery out and went to go get it tested. It had voltage but a CCA of only about 270 which is a failing battery. I bought a new one and hooked it up, and still nothing. All the fuses are good unless I'm missing a hidden one and my headlights do come on but my radio doesn't. So did I blow the ecu, the starter, the alternator, of all of them?

[Benjamin_Button]

Alternator? Wait and see what the experts say

[Alberthype]

I did this a few years back and it ended up being a fried ECU check that!

[claytonH14]

I read in one thread that it fried one guys alternator because of it. How would I check to see if the ecu is fried without having a second ecu?

[prasina2]

Clearly you'll need a second functioning ECU to install and test unless you have actual electronics diagnostic skills.

[oliver.r]

did you check your inline fuse? (fusable link)

[bmwman91]

It could be the fusible link. Find the smaller black wire that comes off of the battery positive terminal and trace it about 2 feet out. There is an inline fuse under some shrink tubing. If that blows, nothing related to the ECU or fuel injection gets power. The engine should still turn over though, so if the starter has also stopped working then the issue is something else.

[rcsoundn1]

He states he already checked the fusible link

[claytonH14]

Yup. I cut open the fusible link and it is still solid. However, today when I was showing a friend what was going on, I did hear a single click whenever I would initially try to start.

[claytonH14]

I put a new ecu in it a few days ago. It still doesn't start but I am getting fewer lighs on my dash.

[bmwman91]

I am wondering if you somehow blew the ignition coils. Can you test to see if you are getting sparks? A quick visual of the coils themselves can also help because if they failed from overheating/over-current, they sometimes melt the epoxy casing. I looked at the wiring diagrams and don't see any plausible way that it could have happened though.

Chances are that you blew out the rectifier diodes in the alternator when you hooked things up backwards. That would basically mean that your alternator produces no current or voltage, although the car should start and run off of a new battery at least for a little while until it drains.

It sounds like you should check to see if you have the basics...fuel and spark. Your symptoms like headlights but no radio make it sounds like a fuse issue. Did you visually inspect them, or get a multimeter out and actually test each one for continuity?