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montmil
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GEN Light Auxiliary Circuit
01/16/13 at 12:28:10
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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.


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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.


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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.


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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.
  

Monte Miller
Denton, TEXAS
1978 BMW R100S
1981 BMW R65
1983 BMW R65
1995 Triumph Trophy
1986 VW Cabriolet
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Adrian
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Re: GEN Light Auxiliary Circuit
Reply #1 - 03/25/18 at 18:16:36
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Hi there - I just wanted to check with you about this circuit. I'm assuming that this is used as well as a light. I have changed to an Acewell speedo/rev counter and fitted a seperate gen light. I would still like to fit this as well - thanks for your advice.....
  

R65 1984
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marcmax
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Re: GEN Light Auxiliary Circuit
Reply #2 - 03/25/18 at 19:45:19
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Hi Adrian,
I fitted an Acewell speedo and a small LED for a GEN light. The LED didn't have enough resistance so I added this mod and have not missed a lick. It has been in place for 4 years now and working perfectly. I did add it to my printed copy of the wiring diagram so I wouldn't forget it is there.
  

Keep your bike in good repair:  motorcycle boots are not comfortable for walking.  

1982 R65ls        1984 R65ls        1991 K75
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Adrian
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Re: GEN Light Auxiliary Circuit
Reply #3 - 03/25/18 at 22:42:31
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That's great & thanks marcmax 😉
  

R65 1984
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Adrian
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Re: GEN Light Auxiliary Circuit
Reply #4 - 03/30/18 at 23:34:45
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Hi again - hopefully the final question - I just wanted to check about the blue wire connection. I don't want to be messing with the 2 wire white connector under the tank - so I plan to connect to the blue wire on the back of the diode board.
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As it's the same wire I assume this is okay - reassurance is needed Smiley
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It's an R65 1984 model - European spec ......
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The surprise for me - was the connection of the resistor. I'm not an electrician but as the gen lamp is connected to the ignition lock (green/black? wire) and the blue wire from the old rev counter plug (I used electrical pins to connect the Acewell to this plug) - I had assumed that the resistor should be connected the same.
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I trust that this connection for the resistor must work - but could you explain why it has a different connection to the gen lamp.
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Thanks .......
  

R65 1984
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