Strange dimmer (hi/lo) switch issue.

arcticXS

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On my 650D I just found a weird issue. Low beam works perfectly, but when switching to high beam, low beam stays on, however the light goes a bit dim. I guess due to the increased voltage drop when both filaments are drawing current. My dimmer switch seems to be a correct European 77 model, with only 3 wires to it. (7 wires total to the entire LH switch assy.)
Both the slider and stationary part seem to have the necessary contacts for a US market switc, I.e 2 switches in 1.
The one that is connected seems to be of a " make before break" design, so both lights are on for a brief moment during switching. Which is generally a good thing. Except that my switch does not disconnect low beam when high beam is on.
Is it possible I have an incorrect slider, or is it just a case of manufacturing tolerances?
The only solution I can see, is to file a bit off one end of the switch plate, and somehow extend the other end, to ensure the low beam disconnects when switching to hi beam. Is there any other fixes? I am definitely open for suggestions here!
 
I have replaced the bulb, no difference. Low beam works as it should, when switching to high beam, low beam stays on as well. But light output is dimmer. As my bike is a European model, the safety feature that automatically switches mode when a bulb blows, is not fitted.
The current path is just ignition switch, RH side handlebar headlight switch, LH side dimmer switch, H4 bulb. Simple as it gets.
 
Low beam works perfectly, but when switching to high beam, low beam stays on, however the light goes a bit dim.
Is it overall dimmer when switching to hi beam? If so, there's probably low resistance to ground in the hi beam circuit. Possibly something with the switch, which could explain why the lo stays on.
 
Applause for 2many! A really silly mistake by me, when connecting my aftermarket headlight. Since we have 24 hours of daylight from early May until early August, I never noticed the weak high beam before recently!
After spending several hours disassembling and scrutinizing the switch, it turned out to be as simple as swapping two connectors :)
 
But only up to the '71 models.
After that, look to Mailman...

Huh? Who....me?
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