[Thud]

My 1990 325iC (126,000 mi) has started randomly deciding not to start. What happens is that sometimes (becoming more frequent) - but not always - I'll turn the key to the 2nd (pre-ignition) position and ALL electrical power will completely cease, and the car - obviously - won't start. The only way I've found to work around this issue is to disconnect the battery, wait a few minutes, reconnect the battery, and try it again (sometimes takes 3 or 4 repetitions of this procedure). It happened once when I stalled it in reverse too, but otherwise never happens once the car is started.

When I bought the car, the "original" (I assume) stereo (which had newer security features incl. code, blinking light, beep) was faulty, so they replaced it with an older (1 or 2 yrs) model which had older security features (incl. code); I'm wondering if this adversely affected the "car-side" security features of the original stereo, and is somehow resulting in faulty activation of a kill switch. Any other ideas?