Elictrical system shut down

09-25-2004, 02:56 PM
I bought a 1988 735i and drove it home (about 70 miles). About 5 miles up the road, the speedometer stopped working. Then, about 10 more miles, the brake lights stopped working. Right after that, the licence plate light stopped working. Then the seat adjuster. Then the passenger side power window. When I got it home and cut the car off, about 5 minutes later, I tried to start it again and it wouldn't. The battery still had power. Two days later, the alarm was still working and the car started. I'm thinking maybe it's the alternator. Any suggestions would be appreciated.

09-26-2004, 08:19 PM
Don't know about this one except stay away from old beemers!

09-27-2004, 02:45 PM
Well, just for the curious, it looks like it was the alternator, which has been replaced. Everything seems to be working fine now.

KC Ron Carter
10-02-2004, 12:11 AM
Too late to help you, but for the lurkers, there are less costly ways to correct a charging issue.

The Bosch alternators have an intergrated voltage regulator brush assembly, that takes 5 minutes to change.

$25 versus $250.

Alternator Regulator

They can wear into a grooved pattern and the impact of driving can make them vibrate out of the normal groove.

Since the regulator has to increase output to jump the gap it does.

You can clean up the slider rings with abrasive paper.

You can get the brushes as a separate part requiring soldering skills or you can get a Regulator brush assembly for $25

Here is a new and old picture for a visual reference.


Some instruction for changing:

It is a very touchy installation and about 5% of the installation end in the ground link bent and the alternator not functional.

You can then remove correct and reinstall the regulator.

The output must be 14.25 or higher on a Volt Ohm Meter not the dash gauge.

Some hints on the regulator change.

Replacing Alternator Regulator

For those who work on their cars and have not had alternator problems, here is a simple action that should save you down-time and significant costs.

Most alternators on German cars fail due to brushes wearing down (as they are supposed to) between 150k and 200K miles. Brush replacement is very easy -- it should not take over 5 min. and the brushes are attached to a new regulator.

To replace regulator assembly -- back of alternator held in place with two straight slot headed screws. This has a round transistor mounted on the outside on Bosch alternators -- the other type is similar but uses different brushes. Pop the regulator out, after removing the screws.

Fitting the regulator back is simple, but you must install it starting at an angle, to assure that the brushes compress when the regulator is flush with the alternator and the screws are tightened.
You are now ready for 200K miles of alternator life.


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