re: E28 dies

[Polands <polands@xxxxxxxxxxxx>]

Matthew,
I've had my '88 535is from 75,000 miles to current 181,000 miles, so
I've experienced a couple of different stoppages.

Since the radio went first, I'd guess that it is not engine ignition or
engine management related. It is probably insufficient electrical power
getting to the ignition control and radio for them to operate properly.

First check the cheap fix: cable clamp connections at battery, clean and
tight.  Second, remove the small wires leading to fuse box from the
positive cable clamp, file the lug contact surfaces smooth, and tin them
with solder, and re-attach everything.  You may indeed have run down the
battery, so jump if need to and see how it goes.

A little more invasive would be to examine the actual copper conductors
in the positive cable from battery to starter motor.  Mine were oxidized
to the point that "the juice couldn't fight its way into the cable"  the
resistance actually melted the lead terminal clamp.  Try replacing this
cable.

A bit more technical would be to use your Bentley manual and digital
Multi-meter to test the alternator.  Mine went south around 170,000
miles, resulting in no replenishment of the battery and eventually no
juice whatever.  This was accompanied with increasingly steady
Alternator idiot light glow.  Replacing this is expensive, but they
don't last forever.  

All of above based on university of been there, done that.
Good luck.

Steve Poland
Portland, OR