This is by no means a complete list of technical hints for your BMW Airhead motorcycle.   The Author’s website has well over a hundred technical articles.  The Author’s website is:
HTTP://BMWMOTORCYCLETECH.INFO/INDEX.HTML

 1. If you are trying to find out if your voltage regulator is faulty, or, bypass it in case of failure while on the road, and thus obtain charging; here is a simple method. I carry one of these ‘tools’ with me in my on-bike tool kit for testing purposes or on-the-road emergencies.

Obtain two each standard male spade connectors. Any autoparts store will have them.  These may be called ‘disconnects’ or ‘push-ons’. Crimp or solder them to a stranded insulated wire about 6 inches long. To use; simply disconnect the plug from the voltage regulator under the fuel tank. Insert the male spade ends of your test lead into the plug’s female openings for D+ and DF; those are the OPPOSED openings. Do NOT connect to the female that has a brown wire. You’ve now removed the regulator from the system and ‘told’ the alternator to go to as high an output as it can…which it will at something like 4000 rpm or so. WARNING, this is for brief testing only or for limping home at low RPM.  This is because riding any distance at high RPM will cook your battery and is also hard on the diode board, and every other electrical item. If your charging output is still low with the jumper connected, you have other problems.