tam162 wrote:Will testing with a 12 volt battery damage anything on a 6 volt system?
Yes! It will fry your light bulbs, probably within seconds. Chances are, sometime during testing, you will forget, turn on the lights and then say OUCH. The brake light is always hot on some models, so accidentally touching the brake pedal might fry your tail/stop bulb.
The generator and voltage regulator are pretty tough units, and normally 12v is not going to hurt them. But here's the problem in giving advise. Does your bike factory stock wiring, in good condition, connected to all the right places? Is your voltage regulator stock and in good condition? If you're trying to diagnose a problem, then something's wrong. What, we don't know. And at the moment, neither do you.
The best thing to do is to get one of the little 6v sealed batteries (See the Technical article on Batteries) for about $10 on Amazon. If you only use it for testing, it will last years and years, and you can recharge it with a 6v BatteryTender Jr. if need be.
If your only option is to use a 12v battery, then disconnect the wires from the regulator's B+ (or BAT) and D+ (or GEN) terminals, and hook your battery positive to the B+/BAT wire, not the regulator terminal. XLCHs don't have them, but K-models and XLH's have a generator indicator light which connects to the D+/GEN terminal. This wire gets 6v when you turn the ignition switch on, and if you're using a 12v battery, you'll be feeding 12v through the light bulb to the regulator and to the generator. Actually, it would fry the GEN light bulb before hurting the generator, but still...
Just a couple of knowledge tidbits.
1) Your voltage regulator has two units in it - a cutout relay which disconnects the battery when the generator is not generating (at very low idle or when turned off), and a voltage regulator relay. When you go for a ride, the cutout relay closes and stays closed. The voltage regulator relay opens and closes around 200 times/second. After 50 years, the spring steel hinge wears out and breaks, and the v.r. stops working. Seldom is there an electrical problem with the regulator - it's usually a mechanical problem.
2) The generator light operates by sending 6v from the ignition switch through the GEN light bulb to the D+/GEN terminal of the regulator, which connects to the armature of the generator. When the bike is not running, the armature is grounded inside the generator. When the engine is running at very low idle, the armature is effectively grounded. Current flows from the ignition switch, through the light bulb, through the generator's armature, to ground, and the light bulb lights. Once the generator starts generating, there is 6v at both ends of the wire, so no current flows, and the GEN light goes out.