2000 750iL various electrical issues

[slm987]

First off, my suspects for all this are the ignition switch, the GCM, the window controller, and the LCM.

Power seat and power steering column don't work. Intermittent cluster function, sometimes I have speedo and no odometer, sometimes I get a check engine and traction control light with a really dim seatbelt light that flashes when I turn on the blinker, and then sometimes I just have nothing at all, it acts like there's no power. The cluster will sometimes regain full function except for illumination when I hit a bump. Climate control comes on and off, blower doesn't work at all. Central locking doesn't work. Windows don't work. Front left blinker and rear right blinker don't work even with good bulbs. The OBC/navigation display acts like it's disconnected and the engine isn't running, doesn't record average mpg, the time and day are blank. Trunk closing assist doesn't work. Car doesn't recognize that the driver and passenger doors are open but detects the rear one just fine. Transmission randomly goes into what I assume is failsafe mode where if you shift into the manual mode it just says 5. The CD changer doesn't work. Lastly, and probably the least of my worries, the driver side vanity mirror lights don't work.

Things I've done in attempt to diagnose: disconnected batteries to reset systems, checked fuses (minus the high amperage ones in the trunk or the ones possibly under the passenger seat). It's honestly easier to list what ISN'T wrong with this car. I don't feel like throwing parts at it until suddenly everything starts working again. Any gurus have any input?

[oldroller]

Pull the passenger seat and examine the power distribution center under the passenger floor carpet. Likely corrosion issues from water (sunroof drains, etc).

[Mayorchuck]

Did these issues start all at once? I've never seen an iggy switch cause all these issues but many of these could point to it. Could be a water issue as suggested or even a bad battery. This car is very picky about voltage.

[slm987]

The top battery looks very new and the car cranks quite happily, no idea about the bottom one though. My friend bought this car from a dealership of all people. It was an Illinois car since new, so corrosion wouldn't surprise me. Also, today I figured out that the obdii doesn't have power going to it anymore. Could it be that power distribution center doing all this?

[slm987]

Also, since neither of the power seats work, how would I go about getting to those fuses? It's far back enough to be able to get the front bolts out, but not the rears... I can make a video of exactly what it's doing later if that would help.

[Mayorchuck]

You will need to hook 12v directly to the seat plug. It will be the thickest red (Power) and brown (ground). Once you do that, you can operate the seat normally. Also check the General Module. It's up behind the glove box. It lays horizontally and has 3 plugs on it. It can also get wet from clogged sunroof drains.

[mikeysentra]

I would start with checking both Batteries; get them both load tested and if either is suspect replace both. My 99 750 had several weird electrical issues and they all seemed from 1 of the 2 batteries were weak. Replaced both and the problems went away.

[carnut1947]

Use a 12 volt power drill battery jumpered at the seat wiring connector to power the seat forward. Once the right seat is out report back on the distribution box.

[slm987]

I thought the general module may be acting weird, door locks not working and what-not. I think an easier way to get the seat to work would be to jumper 12v to the corresponding spot in the fuse panel, my plan was to make a fused lead to go from the jump point under the hood to the correct spot in the fuse panel, and hopefully get power to the seat. Will remove both batteries and load test tomorrow.

[slm987]

Updates, the bottom two terminals on the power distribution box were hoopajooped, the wires just sorta fell out. That got fixed and all is well.