Maintaining the GEN lamp is critical in keeping your BMW Airhead's battery charging. In the rare instances should a GEN warning bulb fail, that little bulb's filament will knock out the exciter circuit of the Airhead charging circuit. Bad bulb. No charge.
Here's how to build and install a solid-state alternator back-up for less than two bucks:
Available at Radio Shack, pick up a five-pack of 330 Ohm, 1/2 watt resistors for just over a buck. A bit of wire, shrink tubing and a zip tie completes the shopping list.Show more
Solder a wire to each end of the resistor leads. I used about one foot each of blue and green/blue as this is the color of the bike's wires you'll tap into. Use a heat sink clip on the resistor leads to protect the resistor from overheating. Cover the soldered joints with small diameter shrink tubing.Show more
Finally, trim down the zip tie and insert it into the larger diameter shrink tubing. The zip tie stiffener will prevent any potentially damaging flexing of the resistor leads.Show more
The install is quite simple: The green/blue wire attaches to the green/blue wire terminal on the ignition coil. Attach the blue wire to the blue wire found in that big, white nylon connector block under the fuel tank. That's it. I always feel better if I detach the negative battery cable when ever I'm doing any kind of wiring chores on my Airheads. This circuit is suitable for 1977-95 model Airhead BMWs.