• Welcome, Guest! We hope you enjoy the excellent technical knowledge, event information and discussions that the BMW MOA forum provides. Some forum content will be hidden from you if you remain logged out. If you want to view all content, please click the 'Log in' button above and enter your BMW MOA username and password.

    If you are not an MOA member, why not take the time to join the club, so you can enjoy posting on the forum, the BMW Owners News magazine, and all of the discounts and benefits the BMW MOA offers?

  • Beginning April 1st, and running through April 30th, there is a new 2024 BMW MOA Election discussion area within The Club section of the forum. Within this forum area is also a sticky post that provides the ground rules for participating in the Election forum area. Also, the candidates statements are provided. Please read before joining the conversation, because the rules are very specific to maintain civility.

    The Election forum is here: Election Forum

Charging issue

miairhead

New member
When I turn the key the red light goes on the quickly out. The headlight is dim also.
Horn, signals, all work, but head light is very dim too, and bright light only comes on with flash position. I checked battery voltage, correct both with key on and off.
 
When I turn the key the red light goes on the quickly out. The headlight is dim also.
Horn, signals, all work, but head light is very dim too, and bright light only comes on with flash position. I checked battery voltage, correct both with key on and off.
Guessing, based on the info so far:

The Gen light going out suggests that the downstream side of the bulb is seeing 12V+ immediately, from some source other than the alternator (the normal source of counter-voltage to put out the Gen light).

The headlight only working on the flash-to-pass position, and only a dim low beam, suggests that there is little juice passing into the headlight switch via terminal 56 (the supply wire to output circuits 56a and 56b). The feed to terminal 56 is from the load relay relay (the relay that turns the lights off during starting).

My first guess is that there is a short between the supply wire from the load relief relay to the headlight switch, and other circuit (not necessarily the Gen light circuit, as that would still allow 12V to pass to the headlight switch).

I'd suggest first rubbing/moving the wiring harness between the headlight bucket and the frame and the harness between the headlight switch along the handlebar -- with the ignition on -- to see whether the headlight and Gen light come -- i.e., looking to see whether there is a short in a harness (a easy/quick to do). If no, then proceed to pulling the headlight to look for obvious shorts/worn-off wire insulation, etc.; same with the electrics under the tank next. You may want to focus the search a bit by identifying the load relief relay and starting to trace the 56 wire from the relay to the headlight switch to see where the 56 wire may be shorted.
 
Switch?

I take the light switch apart, hold it a certain way, ALL is good. I have no idea of why a light switch would effect the charging. I order a new switch, I do not see what the issue could be with the switch. Just effect charging?
 
I take the light switch apart, hold it a certain way, ALL is good. I have no idea of why a light switch would effect the charging. I order a new switch, I do not see what the issue could be with the switch. Just effect charging?
I suspect there is nothing wrong with the charging circuit. Rather, I suspect a wiring issue associated with the headlight circuit, which is causing the charging light to be prematurely extinguished.

The headlight switch is in a cluster with other bits present -- all it would take is a short across wires in the harness or between switch contacts to have 12V passing backwards through the Gen light circuit (thereby extinguishing the bulb, as the bulb would see the same voltage at both terminals, i.e., no current flow to cause th ebulb filament to glow). I imagine that if you used a continuity meter across the terminals in the wiring harness at the plug-in end, you would fine connections across circuits which should not be present.
 
Back
Top