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On my way to work the other day a guy pulled up next to me and told me my tail light was not working. Later that night randomly my headlight stopped working and when I got it to my garage I pulled the key and it continued to run. It seems to me random. After messing around with the wires I got the head light and tail light to work but the neutral light and brake light is not working. And again after pulling the key it remained running. R50/2. Any help would be greatly appreciated!

When the key is pushed in on a /2 a set of contacts on the switch closes to complete the circuit of the magneto to ground turning the ignition on. If those contacts stick together, pulling the key will not turn the ignition off. The light issue is probably caused by corrosion in the switch too. Spraying contact cleaner in the switch and working the switch might help.

Thanks!!! I'll give it a shot!

George Ryals wrote:When the key is pushed in on a /2 a set of contacts on the switch closes to complete the circuit of the magneto to ground turning the ignition on. If those contacts stick together, pulling the key will not turn the ignition off. The light issue is probably caused by corrosion in the switch too. Spraying contact cleaner in the switch and working the switch might help.

That is Bass Ackwards.
The key, when pushed in on a /2 (remember it's a Magneto bike) DISCONNECTS the ground wire from the coil, allowing the magneto coil to operate.
When the key is pulled up it grounds the coil, killing the spark.

So, wirewrkr , what's your solution to his problem?

Start with a good schematic. The factory one is dandy.
Clean contacts in the switch and take the time to understand how it works.
It has two related but unrelated functions in it.
When the key is up it is free to spin around and isn't able to turn the tumbler that actualy swings the contact bar to the different functions. When pushed down it can now turn the tumbler, and at the same time pushing down on the contact point opening it so that the magneto is no longer shorted out.
The 18 g brown wire w/black stripe is the magneto kill wire. \The system is very antiquated but extremely simple and easy to understand. Those contacts can usually be cleaned without removing the headlight completely, I have disconnected the speedo cable and handlebar switch and unbolted the headlight. Then you can flip it almost all the way around so you don't have to stand on your head to see the contacts. The next phase is checking and cleaning the contacts at the other key locations, such as the brake light switch and the one behind the battery. Go through the trouble to unscrew and pull each wire out to inspect it, make sure there is no corrosion and that the tinning is still in place.
Next is the bulb holders. On a 6 volt system the tiniest bit of resistance will inhibit the function of the lights.
remove bulbs, clean all contact areas, tighten all sockets so they make a nice clean contact.
Now would be a really good time to take a close look at all the harnesses for overall condition.
The original headlight switch harnesses were notorious for causing shorts because the wires were rubber coated instead the more durable plasticy material and would crumble inside the casing causing shorts.
Check these out.
http://www.wirewerkes.com/WIRING_1951-69_BMW_55EM.html
Robert

wirewrkr wrote:Start with a good schematic. The factory one is dandy.

You said it brudder! Can't get there without a good road map!!

First check the switch plate to make sure that it is mounted up tightly against the stops. If it is loose, then the grounding wire for the magneto doesn't get shorted out. The bending of the contacts should be the last choice. They are usually OK.

Duane Ausherman wrote:First check the switch plate to make sure that it is mounted up tightly against the stops. If it is loose, then the grounding wire for the magneto doesn't get shorted out. The bending of the contacts should be the last choice. They are usually OK.

Wow, is Linda answering tech questions for you now too?

Linda knows more than I do, so she is taking over.............. or so I allow her to think:-)