Topic: 1989 NT650 headlight issue

[thrutheframe]

I'm working on a 1989 NT650 that the headlight doesn't work.  At the headlight plug without the lamp, I get 12v on both low and high beam by metering +'s to the ground in the plug and by metering + to the ground lug under the seat.  Lug under the seat to ground in the plug is .265 -.268v.  The lamp is good /brand new I tested it by connecting it directly to a battery.  When I add the lamp, I get nothing and when I meter across + to ground at the plug I get 0v.  When I meter the +'s to the lug under the seat I get .265 -.268v.  It makes no sense.  This is a pristine, garage kept bike that belongs to a meticulous collector and the only alteration is he had a head light modulator (flasher) that he was running for a while.  My tests do not include the headlight modulator. 

Any suggestions on where to look next?  I took the seat off and cleaned the ground lug hoping that was the issue but it was decent and I cleaned it further to absolute bare metal and reconnected it.  The rest of the lighting system works fine.  I get the same results with an incandescent bulb.


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[Steve_K]

I would suggest looking at the start button on the handle bar.  There is headlight turn off when the starter is used.  I had that happen on my 550 and my 88 Hawk GT.  Put switch in or resolder the wire at the button.
Steve

[thrutheframe]

Yes I'll be looking at that but like I said the headlight plug has 12v on it until you add a lamp.  I'm thinking comprised wiring.


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[MoMo]

Make sure the resistance from the green headlight wire to ground is zero ohms...Larry

[thrutheframe]

I would suggest looking at the start button on the handle bar.  There is headlight turn off when the starter is used.  I had that happen on my 550 and my 88 Hawk GT.  Put switch in or resolder the wire at the button.
Steve

Steve you nailed it.  The switch when open should read 0 ohm / continuity.  It reads 155 ohms.  The load is too high to allow the light to work but still has 12vdc.   

A gremlins worth of resistance.


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[thrutheframe]

It was full of brown velvety crud.  Compressed air fixed it.  Reassembling bike tomorrow


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