Hi Dave,

Although it could be the alternator rotor coil open, odds are it is just the brushes no longer reach the slip rings. The Bentley manual, a recommended book on your 240, suggests the brushes should be replaced if they fail to protrude more than 5mm from the holder. I think they are a little generous considering the slip rings have worn some too.

While you are in the yard getting that hard-to-find-elsewhere adjuster bolt, you can pull another regulator assembly, giving you a spare. You can get new Bosch brushes for a couple dollars and change them on your spare if you like, or spend 30-some on a new assembly.

Actually, if you want to check for the open rotor coil, and save yourself pulling the alternator, just sneak your test probes through the regulator opening and measure the resistance between the slip rings.

I went to pull a regulator for a spare once, and found a 740 car in the yard, a model where the alternator is up high and clean on the intake side of the motor, so I just pulled the alternator whole. That may be your best source for the adjuster bolt too.

--
Art Benstein near Baltimore

A chicken crossing the road is poultry in motion.