[Villancj_]

Lemme take you on my lil journey,

Last week my car wasn't starting and I let it sit for 30 mins while I phoned a friend for a jump. Literally as he was pulling up I started the car and it worked, however once leaving the parking lot my windshield wipers came on, every light imaginable on a BMW came on and my infotainment center turned off and my speedometer wasnt working. The car died as I was getting on the on ramp and I phoned that same friend to get a new battery at O'Reillys. Put the new battery in and drove home. Easy.

Two days later I took it 45 mins to see the gparents and it threw every light and lost power as I was coming home... I towed the car to a friends and just now replaced the alternator today after a week of sitting. Car still isn't starting and stuff like pressing the brake to turn the ignition on turns all the lights OFF. WTF? We tried to jumpstart it but it wasn't getting any power at all. Still the same crappy lights

I turned the car off and was having a conversation with my friend behind the car and then the taillights started flickering on and off so I just disconnected the negative terminal and well, here I am.

My theories: fried ECU/DME or somethings screwed up with the cables that run from the battery to the front of the car. I'm not an expert (obviously) but I came here to see if anyone has experienced something similar or what some possible ideas are to help me fix it. Thanks!

[Steve Sas]

Wasn't there a issue with main power supply in the early days of these cars?

https://www.e90post.com/forums/showthread.php?t=820317

Also may want to check for water in the DME box.
And theres the corroded connections behind battery due to water leaks in trunk.

[tcphoto]

You cannot just throw new parts at a problem, it can get rather expensive.

[e91Owner]

Originally Posted by Villancj_

Lemme take you on my lil journey,

Last week my car wasn't starting and I let it sit for 30 mins while I phoned a friend for a jump. Literally as he was pulling up I started the car and it worked, however once leaving the parking lot my windshield wipers came on, every light imaginable on a BMW came on and my infotainment center turned off and my speedometer wasnt working. The car died as I was getting on the on ramp and I phoned that same friend to get a new battery at O'Reillys. Put the new battery in and drove home. Easy.

Two days later I took it 45 mins to see the gparents and it threw every light and lost power as I was coming home... I towed the car to a friends and just now replaced the alternator today after a week of sitting. Car still isn't starting and stuff like pressing the brake to turn the ignition on turns all the lights OFF. WTF? We tried to jumpstart it but it wasn't getting any power at all. Still the same crappy lights

I turned the car off and was having a conversation with my friend behind the car and then the taillights started flickering on and off so I just disconnected the negative terminal and well, here I am.

My theories: fried ECU/DME or somethings screwed up with the cables that run from the battery to the front of the car. I'm not an expert (obviously) but I came here to see if anyone has experienced something similar or what some possible ideas are to help me fix it. Thanks!

When you get a new battery, you need to register it with any number of software options. I don't think that alone is the cause of your problems, though. Scanning the car for faults will give you a better idea of where to look for the root cause.

[jericho_17]

wire insulation start to crack everywhere in these cars specially where there is heat, but sometimes finding the palce where it cracked could be very complicated

[tenzen11]

Check behind the fuse panel in the glove compartment, that battery cable behind it that runs from the trunk can sometimes get really hot. Warped plastic in the back would be a good sign of damage to some of the contacts even though the fuses will look ok.