Electric troubleshooting

Classic short-frame models

Electric troubleshooting

Postby Otis » Tue Nov 05, 2019 8:21 pm

Need to troubleshoot a non working brake light on a magneto XLCH. Short of checking continuity or leaving the bike run forever is there anyway to test the electrical system? I’m wondering if a 12v battery can be temporarily spliced in for troubleshooting purposes without harming the voltage regulator and which wires to hook the battery to? Also if the generator needs to be polarized how do you do that without a battery to flash it to?
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Re: Electric troubleshooting

Postby hennesse » Wed Nov 06, 2019 9:40 am

Otis wrote:Need to troubleshoot a non working brake light on a magneto XLCH. Short of checking continuity or leaving the bike run forever is there anyway to test the electrical system? I’m wondering if a 12v battery can be temporarily spliced in for troubleshooting purposes without harming the voltage regulator and which wires to hook the battery to? Also if the generator needs to be polarized how do you do that without a battery to flash it to?


If you connect a 12v battery, negative to frame or engine, and positive to voltage regulator B+ terminal, you will then have an XLH.

The voltage regulator contains a cutout relay that connects the regulator's B+ and D+ terminals to each other - once the generator output reaches a certain level. With the bike not running, there's no problem, since the B+ terminal is only connected to the head/tail-light switch and the brake light switch. (See the wiring diagram in the Technical section). Then diagnose your brake light problem to your little heart's content.

To polarize the generator, take a short piece of wire, and connect the voltage regulator's B+ and D+ together FOR ONE SECOND. That's all it needs. All this does is magnetize the iron pole shoes inside the generator - in the correct direction. It does not hurt anything to do this, so do this any time you've taken the wires off the generator, let the bike sit for years, etc. (For models with the Delco-Remy regulators B+ is BAT and D+ is GEN)

Actually, there's no problem leaving the battery connected with the bike running. Once the engine gets up to speed, the generator will charge the battery. Turn the bike off, and the regulator's cutout relay will open, disconnecting the battery.

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Yes, you can use a car battery. I made a set of jumper cables by taking 12' of red and black 16-gauge wire. Put one end of each wire in a vise, put the other end in an electric drill. Keep the wires stretched and slowly run the drill until the wires make a nice spiral. Get some battery clips (Amazon is your friend) two small ones for the motorcycle battery and two larger ones that will fit car or motorcycle or whatever voltage donor you might need to use. On our AMCA chapter outings, there's often one dead battery in the crowd. Note that twisting the wires will shorten them - if you want 10' cables, start with 12' wires!
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Re: Electric troubleshooting

Postby Otis » Wed Nov 06, 2019 12:44 pm

Thank you. Some good information. I did figure out last night that the B+ was the positive and chassis was the negative and was able to energized the electric system. Only the horn didn’t get powered which appears to run straight off the generator with a capacitor boost but I really didn’t get that far yet. Just to be safe I unhooked the 2 red wires off the regulator before doing this.
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Re: Electric troubleshooting

Postby tam162 » Wed Nov 06, 2019 1:21 pm

Will testing with a 12 volt battery damage anything on a 6 volt system?
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Re: Electric troubleshooting

Postby Otis » Thu Nov 07, 2019 1:06 pm

It will damage the 6v bulbs. A 6v battery will work.
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Re: Electric troubleshooting

Postby hennesse » Thu Nov 07, 2019 1:57 pm

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.
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Re: Electric troubleshooting

Postby RFREES1 » Thu Nov 07, 2019 2:01 pm

Hi Otis,
If you have a 6V 6 to 10 Amp battery charger I would use that to test your system. If you do have a short the battery could melt your insulation on the wires. Most Battery chargers have a circuit breaker built in to there system. The small clamps on the battery charger will hook up to the regulator the same way that was mentioned to hook up the battery. Good Luck.


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Re: Electric troubleshooting

Postby Otis » Thu Nov 07, 2019 3:30 pm

The question about 6v should be directed to tam162. That wasn’t my question, in fact I replied it will ruin the bulbs. I’m working with a 12v system and everything is figured out. The -67A brake light switch is sticking (near impossible part to find) and the low beam not working was due to a faulty dimmer switch. Thanks for the help, all will be fixed soon.
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Re: Electric troubleshooting

Postby JerrryR » Thu Nov 07, 2019 8:20 pm

Hi Doug, I'm feeling bad that the 67A switch I sold you is sticking. I have one NOS switch left. PM me your address and I'll send you the new one. Send the old one back to me when you get the new one. Hope all is going well for you.
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