Hoping that someone can help. I'm a newbie to airheads and haven't really done any wrenching in years. This bike was a garage find, had been sitting for about 10 years and was in pretty poor condition with not much working. Speedometer shows about 52000, but from the condition of the bike and the wear on it, it could be 152,000 or even 252,000. In the past 3 months I've taken it mostly apart and put it back together so now it runs and rides. All lights work and the bike starts up on the first try and generally runs well. The problem is it's not charging and there is no generator light. I have replaced the following: Battery, Rotor, stator, voltage regulator, Diode board and most of the connecting wires. I've also replaced the old instrument pod circuit film with a new Katdash led unit. I've tried to follow the published troubleshooting as best as I could and can't get the light to light at all. I've checked terminals in the instrument pod and all seem to be functioning correctly. As far as I can tell, there's not much left to replace. Any suggestions would be greatly appreciated.
Welcome, and glad to help ! Here's 3 suggestions in order of importance....
1. One of the quirks of the BMW charging system is that the alternator will not work without a working warning lamp. When the bulb burns out, then the charging system stops working. Check the #194 bulb in the instrument cluster. This is a common bulb you can get from your LAPS. Do not fit an LED, it requires the resistance of a working incandescent bulb.
2. Although the OEM voltage regulators are sealed, they are still mechanical and give up after 40 years. I suggest one of the new adjustable solid state regulators. These are especially helpful if you installed an AGM battery in place of the original "flooded cell" type. AGM batteries require a slightly higher charge voltage than the original regulator is capable of, so you'll be "killing 2 birds with 1 stone".
3. Try new alternator brushes. Easily changed by removing the front engine cover.
► Items 2 & 3 available HERE at the very bottom of the page.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Charging Problem Solved!
Thanks for the responses guys. Much appreciated. I do have the book mentioned on order.
It appears that I had two problems. After replacing almost everything on the electrical system and still no Gen light, I figured it had to be a problem in the cord before it attaches to the instrument pod. I installed the resistor bypass between a 12V positive source and the blue wire at the VR to bypass the gen light. Then after hours and hours of studying all of Snowbum's info on the charging system, I finally focused on his discussion of a reverse magnetized rotor. So I rigged up a jumper, grabbed an old battery cable from the pile of parts and touched connected the battery briefly to the DF terminal for the rotor. After starting the bike, the multimeter showed just over 14 v when I rev'ed it over 3000. The Generator light still does not come on, so bad wire in the cord bundle is indeed likely. I have connected an inexpensive LED voltage regulator to the handlebars so that I can monitor the charging system. Now it's time to tackle all those other issues on the list!
Very cool solution. Congrats !
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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