The gremlins are afoot, allright!

Have you 'spun' all the in-cabin fuses to remove any oxidation on the tips? Fuses can look just fine and still be intermittent.

I converted an alternator external regulator to an internal on one of my earlier 240's. Look on the back of the alternator for a black diamond-shaped housing held on with two bolts, one at each point of the diamond shape. That's the internal regulator and brush assembly. It can be removed with the alternator on the car. Unhook the battery negative cable first. If the brushes are shorter than 2mm, replace the set.

While the brush unit is out, look in the hole - use a flashlight and mirror - and check the condition of the slip rings. Heavy black arcing marks may mean a new alternator is needed. Very uncommon. Also be looking at how you will have to finagle the brushes back in there.

This might help. Post back with any progress.

Good Luck,

Bob

:>)