Uknown power flux
 

I have a '95 318ti, 4cyl, 2 dr. All stock. I've been having this power issue where first my stereo will lose sound, then die all together. Then the ABS and battery light will come on, shortly after the entire dash will die. No RPMs, no MPH, no milage, natta. Even the outside temp will warn me saying it's 4F or 16F (wtf??) Then the car itself would die.So first I test the battery-bad cell=replaced battery, but still same prob. Then replace alternator (which looked and felt like it really needed it) which did seem to help or at least prolong the car from dying. So now I still have the problem of stereo dying and my ABS light coming on and temp going wacky, but my RPMs maintain now and I feel I could drive it but the longer I drive it the worse it gets, then when I stop it seems to slowly recover. Like I'll sit in the driveway after a spin and the stereo will eventually work again.
SOoo...any one got any ideas of what to do? I plugged it into an analyzer and got codes for a fuel pressure reg, fuel filter (bought but not in yet) and oxygen sensor.

And then...
 

I failed to add that the car will still die. I took it around the block twice. First stereo dies, then ABS light, then turn signals won't work, then the temp outside drops instantly to 16F (lolz) and the dash dies and engine dies, gliding me to a halt. But when I let it sit for 30-45 mins and try to start it, it will start allowing me to go x distance until the issue repeats...
I'm thinking maybe a relay, or fuel pump issue? but it seems more electrical than anything...
Please help, this is driving me mad.

sounds like a ground problem

Any idea where that ground problem could be? I thought of that too but not sure where to start.

Somewhere in the wiring :) Start at the battery cable and work your way around. There is a round that goes to the motor mount and a few right at the battery tray.

I was having a problem with the steering column not unlocking so I took that apart to fix that, also hoping to find the ground problem there but wiring is perfect. Followed all of the wires from the battery around to check ground wires and other ground wires I could find but all seem good thus far. I'm thinking maybe the ABS warning is a clue to where my ground problem is? Do you think maybe a relay is bad or...? Just shootin ideas around.