Generator Light Auxillary Circuit
For all BMW Airheads 1970 through 1995 $3.50
This little piece of wire could overcome the one rare type of charging system failure lots of people aren't even aware of:
The Bosch alternator systems used on BMW motorcycles are designed with a warning light that is part of the rotor exciter circuit. If the warning light bulb goes open circuit from burning out or vibration , the alternator will likely quit charging. This is a very rare occurrence, but can really be a problem if it does happen. At least they DID provide a warning light, unlike a lot of other motorcycles which provide the rider with no clue as to the operation of the charging system.
This generator light bypass circuit utilizes a 330 ohm, 1 watt, metal film resistor securely soldered into color - coded wires to provide a parallel path of higher resistance that would take over in the unlikely event of bulb failure. The resistor is covered securely with glue-filled heat shrink tubing over a piece of nylon cable tie for rigidity. Two tap - in connectors are provided for easy installation with the instructions provided.
NOTE : It is strongly advised to use this bypass circuit only on bikes that have a volt monitor of some sort fitted . Without a second source of information about battery voltage , it will not be possible to know if the generator light bulb is failed or if there is an alternator problem . If the bypass circuit is used without a voltage monitor , and the red GEN light does not light before or after the engine is running, then the charging system output must be checked immediately.