2005 BMW X5 3.0i - Electrical power loss randomly

[Saberlash]

Hi,

I have recently changed my alternator after it died on me. I got a remanufactured one and it seems to be working fine ever since I changed it. The problem is that now sometimes (it happend twice in 4 days) when i start the car, everything powers up but when I turned the key to start (final position where you start the car) the whole power in the car just vanished. Nothing electrical worked anymore. It's like a blow fuse but nothing is wrong with the car.

History:
- I had a sound system installed by me in the trunk which replace the spare tire. I manufactured from MDF a board that sits on top of the battery on the same 3 metal beams that supported the spare tire area. All amps are connected to the battery via a power distributor and fuses.
- All was fine until my alternator died.
- When I had to unplug the battery to change the alternator, i had to lift the MDF board along with all the amplifiers (3) that are probably in total ~80 pounds.By lifting it, I think I might have damaged some of the red cables that go through the back of the spare tire area, near the back passenger seats.
- After I put back together the car after installing the alternator, i connected the battery again, connected the amps and all was fine. (this was Monday evening).

Problem Occurrence 1:
- I drove to work next morning and when leaving later that night for home, I put the key in the ignition and moved into the position where all the lights turn on on the instrument cluster. After a few seconds, I turned the key to start the engine. Instanly, all electrical power went offline. Nothing worked. No alarm, no windows, no central locking, no light, nothing. It was as if I disconnected the battery again.
- I had someone drop me off home that night and when I came back to my car the next morning with my tools, i started trying to reach the battery to see if maybe the battery was disconnected.
- I unscrewed the platform for the amplifiers and lifted it again (pushing on the red wires probably) to look at the battery and make sure it was not disconnected. All was fine, but the power was still offline.
- I looked at the power distributor and I had a "wild" tought to try and unhook the amps from the power, see if this fixes the issue. After unhooking the 2nd amplifier, there a small spark when disconnecting it and power came back on in the car.
- So, after ~14 hours of being "dead", the car had power back on and the battery was still full and I started the car without issues. After about 3 minutes of leaving the car on so that the battery can charge a bit in case it was drained a bit (i'm overcautious) I stopped the car and hooked the "trouble" amp again and the car started just fine, the music was running just fine again.

The car ran fine until...

Problem Occurrence 2:
- Friday evening before leaving for work, I put the key in ignition, instrument cluster lights up like a chrismas tree again and I have a gut feeling it would fail me again for some reason. I turn the key and again the car electrical power goes offline.
- I go in the back and remove the subwoofer and the top of the trunk area to reach the amps.
- I disconnect all amps but the power still didn't come back on
- I proceed to unscrew the platform and I lift it to again look at the battery.
- After some wiggles and putting back the platform, I notice that (again) I have power in the car

My question is: what causes the car to go into a sort of electrical protection mode and not suck dry the battery?
If any of the amps would have been faulty and tried to short circuit the car, they would have burned the fuses, no? The amp in question has fuses on the distribution block and fuses on itself.

Thanks in advance

[cn90]

I suspect the ignition switch (the electrical part on the LEFT of steering column). Tons of info on E39 (5-series) forums.

If you suspect the ignition switch, use only BMW brand PN 61326901961, about $70 at dealer:

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