The New And Improved Unofficial R65 Forum V2
Technical Discussion => R65 Technical FAQ/Procedures => Topic started by: montmil on January 16, 2013, 12:28:10 PM
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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.
(https://bmwr65.org/smf/proxy.php?request=http%3A%2F%2Fbulk-share.slickpic.com%2Falbum%2Fshare%2FkuxxQTZNMQxjNQ%2F3184472%2F800%2Fp%2F3184472.jpg&hash=42715d1736c8150c7796d7e549daf12c91721e01) (http://www.slickpic.com/s/kuxxQTZNMQxjNQ/BMWGENLampCircuit/photo#3184472)
Show more (http://www.slickpic.com/s/kuxxQTZNMQxjNQ/BMWGENLampCircuit)
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.
(https://bmwr65.org/smf/proxy.php?request=http%3A%2F%2Fbulk-share.slickpic.com%2Falbum%2Fshare%2FT2Ac2MjcjO%2CwYN%2F3184477%2F800%2Fp%2F3184477.jpg&hash=848e35a01b73951af1ef13e5b54295629c6a0a9b) (http://www.slickpic.com/s/T2Ac2MjcjO,wYN/BMWGENLampCircuit/photo#3184477)
Show more (http://www.slickpic.com/s/T2Ac2MjcjO,wYN/BMWGENLampCircuit)
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.
(https://bmwr65.org/smf/proxy.php?request=http%3A%2F%2Fbulk-share.slickpic.com%2Falbum%2Fshare%2FywjTxxMUMOgNyA%2F3184470%2F800%2Fp%2F3184470.jpg&hash=6fb12e2dd976158023690d9e6abd96ac8d4fde98) (http://www.slickpic.com/s/ywjTxxMUMOgNyA/BMWGENLampCircuit/photo#3184470)
Show more (http://www.slickpic.com/s/ywjTxxMUMOgNyA/BMWGENLampCircuit)
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.
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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.....
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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.
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That's great & thanks marcmax [ch128521]
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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 :-)
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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 .......
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Hi I have two questions... I have been reading snowbums writeup on this topic and near the end he mentions using a higher wattage resistor to more closely mimic the charge circut produced by a lamp, have you found any negative using the lower watt resistor described in your post?
Secondly, do you have a picture of the resistor installed? The article from snowbum says to connect to an unused male spade connector at the "terminal" of the ignition coil, and the other side to a blue wire coming out of the voltage regulator plug. If I could "see" this or your install I think I would be able to duplicate.
Currently I run an LED and rev the (warm) engine to start the charge... I know this is not a great way to accomplis the task
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Doing the calculation.5W is a little to small but not being used much shouldn’t be a problem