Battery Light R100R

[diloret2]

Hello All,
New to the forum and new to BMW bikes. My uncle had 2 when I was younger (R69S and a R75/6), so I have always wanted to own one. Finally got my hands on one, a 1992 R100R, that had been modified a bit. Long story short, the stock gauges/lights were long gone. I have since fitted a Koso EX-02S gauge, with the N, Signals and Oil lights all functioning. Now, I know my bike had a 'Battery' light, and I believe it is the blue wire in the headlight bucket that hasn't been hooked up to anything yet. My question is, I have read on other generation bikes, that if the 'GEN' or 'ALT' light isn't hooked up, it's not charging your battery. Is this true for my generation of bike, as well? I have a volt meter on my gauge, and it shows over 13.3-13.5V when I'm running at speed. Also, I hooked a MM up to the battery and revved the engine, and the voltage at the battery went up from 12.8 to 13.4, so I am assuming it is charging. I've gone several hundred miles, mostly on the highway, so I feel if it wasn't charging, it would've been dead a long time ago, but stranger things have happened! Any help would be greatly appreciated!

[schrader7032]

Welcome to the forum! I'm not familiar with the Koso EX-02S gauge and how it interfaces to the bike. And you're right, if the GEN light circuit is not properly connected, you shouldn't be getting any charging. The light circuit provides an influx of current to help boot-strap the alternator once the RPMs get up. Mid 13v's is sort of OK, but it should be around 14v for solid long term charging. I don't think you'd be able to add say extra lights or a heated jacket to the bike...it would certainly not charge. There must be some passive current that is somehow getting to the rotor for it to work as it does.

Snowbum has an article on his website about a modification to the charging circuit. If on a stock bike, the light burns out, the battery won't be charging and the rider wouldn't know. So, he suggests a resistor placed in the bike's wiring will bypass the GEN light to ensure there's a path for the current. His article is here:

https://bmwmotorcycletech.info/genlampresistor.htm

[diloret2]

Awesome. I have both wires that go to the battery light in the headlight bucket, so I will jump them with a 470 Ohm resistor. Thanks very much for the info and link!