Funky High Beam Switch

[viking4christ]

1978 GS550. Love it. When the bike is cold and I start it with the headlight on and the beam set to low all is well. I can switch the beam back and forth from high to low. But after about 90 seconds, no matter where the beam switch indicator is set, the high beam will automatically come on and I can no longer switch to low beam. Not a huge deal as I will continue to be able to see everything all the time. Not so good for the person in the on-coming lane.

Any advice would be greatly apreciated.

[chef1366]

Clean the switch and take a look at the headlight connections in the headlight bucket.

[viking4christ]

Headlight connections are fine. I ordered another left hand switch (used) and tried to see if that was the problem. Nothing. Then I got to thinking, my charging system is not working (of course), so I purchased the recommended parts and have replaced and rewired my stator/ reg./ rectifier. I am waiting on two seals to come in before I can put the oil back in and start it up. However, while it was sitting there, not started, I turned the ignition to "on" and tried the same high beam trick, this time there was no problem.
Could it be that my charging system was overloading and causing my high beam to come on all the time? Hmmmm. More tricky business with the Suzuki electrics.
I should have it all back together this week and I'll let you know if that was the deal.

[txironhead]

These bikes do have that crazy overload circuit that goes to the headlight, so you may have solved the problem there. Of course, with a Honda regulator conversion that's all bypassed.....

[tomm]

Thinking it might be a bad ground on the headlight. Don't know where the headlight ground connects, but since that post is common to the both the high and low beam, if it opens up, then current for the high beam will go through the low beam and vice-versa. If it can then find some path back to ground, maybe through another light or a relay or something else connected to the same ground or hot, both filaments could light.
If you can get a probe on the negative post of the headlight, measure the voltage when the problem occurs. If you have anything but zero, you need to either fix the existing ground or add another ground wire. You could also try running a separate test ground to see if that helps.
When grounds open up, all sorts of strange things can happen because pretty much everything is connected to ground on one side. With an open ground, current starts taking some strange paths through things, like water suddenly finding its path downhill blocked, with all sorts of unpredictable results.

[Redman]

Have you concidered the possibility of this being related to the bulb itself ?

Since this happens a period of time after its turned on, that makes it sound heat related, like after the light on for a while and heats up, then somehow the two filemants touch each other and you are actaully getting both hi and low or maybe one and a portion of the other. Or maybe someplace else in the bulb, like in the base of the bulb, after it heats up, something changes and the two leads come into contact. Anyway, something heat related in the bulb itself.

Just an other possibility to concider in your troubleshooting.

[viking4christ]

Ok, so the bike is running again. Still the same deal with the high beam. I have not yet added an aux. ground to the bulb area...I'll do that soon.
Here is my new question...I bought a regular auto headlight for this bike that was the same for all I could tell. Could that have something to do with it? My old bulb said "motorcylce" on the lense.