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New headlight then POOF

motogtp

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1978 Super Sport with 6,000 miles. Low beam was out when I bought it but high beam worked. I bought a new head light and installed it but did not install it in the bucket while I tested it. Right off the bat the low beam works but I notice a little bit of smoke inside the glass so I immediately switch to high beam, which works, then shut off the ignition. When I turn it back on, no low beam, but when I jiggle the connection it comes back on for a bit and then nothing (high or low). Glass now full of smoke. Connection blades look good. Tail light and turn signals work OK. Fuse looks good but what would cause enough over-voltage to burn out the headlamp elements? I went through the electrical threads in The Garage and didn't find a similar topic discussed.
 
I know this sounds dumb but is the lamp marked 12volt? Could be a 6. Use a meter on the leads should be between 12& 13.5 volts. Engine running when blown or off?
 
I know this sounds dumb but is the lamp marked 12volt? Could be a 6. Use a meter on the leads should be between 12& 13.5 volts. Engine running when blown or off?

Engine was off but had been running 30 minutes earlier. I didn't check the voltage but I got it from the Vintage CB750 store so I assumed that is not an issue. Looks like I need to break down and buy a multi-meter.
 
The 750 charging voltage is actually 12 to 14.5 volts.:thumbsup: It shouldn't reach 14.5 till 3000rpm and above. Most 750 will show only 12 volts at idle. My first thought also was that it was a 6volt headlamp. With smoke in the glass I am thinking it was a defective lamp if it was indeed a 12 volt bulb.
 
Dirtdigger - you could be right. What bugs me is that the fuse wasn't blown so I am wondering if I have a short to another energized wire. I think it's time for some professional help.
 
Do you still have the old bulb that high beam worked? If you did you could plug it in and see if high beam still worked, if it blows now then you know you have issues. Smoke in the bulb most of the time indicates a manufacture defect. Smoke means fire which means oxygen which means a bulb that was not made correct because they should be drawn in a vacuum. If you would be shorted to another energized wire it would just be on at the wrong time, it wouldn't increase the voltage. It would probably blow fuses also if you have power circuit shorts. Just a thought. Hope you have a good bike shop to take it to for the professional help, around here I wouldn't trust any of our shops to change a light bulb :laugh:
 
You make a great point. That unit is sealed so there shouldn't be any smoke. In fact, the glass is all fogged up with what look to be "smoke paths" at the top. I think I will pursue a return. I will try the old bulb tonight. I have a friend that has recommended a couple of good independent cycle mechanics. Not too impressed with my local shop so I know what you mean.
 
Dirtdigger - just thought I would let you know that I plugged in the old headlight last night and it worked. Definitely a defect in the new one. Now I am curious to see the response from Vintage750.com. Hope it is a good one.
 
Do you still have the old bulb that high beam worked? If you did you could plug it in and see if high beam still worked, if it blows now then you know you have issues. Smoke in the bulb most of the time indicates a manufacture defect. Smoke means fire which means oxygen which means a bulb that was not made correct because they should be drawn in a vacuum. If you would be shorted to another energized wire it would just be on at the wrong time, it wouldn't increase the voltage. It would probably blow fuses also if you have power circuit shorts. Just a thought. Hope you have a good bike shop to take it to for the professional help, around here I wouldn't trust any of our shops to change a light bulb :laugh:

Finally put the new one I got from Vintagecb750.com. Worked like a charm.
 
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