77 "D" No Headlight voltage, Where is this resistor located?

[jpdevol]

The signal cancelling unit (46 above)is under there too, as I remember, but it has 5 wires, this mysterious resistor should have but two: Y/BK & Y

 

[Slimbob]

Hi All, Thanks for the input. I'm off to the shore for a few days, so I'll have to check later in the week.

Thanks again.
Will keep you posted.

Slimbob

 

[Nelson]

It was a safety feature JP. Imagine riding down a dark country lane at night and the headlight dies on you.... on a tight curve no less. This system automatically switched power to the high beam.... at a reduced current so it didn't blind oncoming traffic. At the same time it turned on the headlight fail light to let you know the low beam died.
I've got it set up and working on my SG. and it really works as advertised.
You gotta remember the era this came from. Automation was a "thing" back then. Everyone wanted to get in on it. I reckon that given the tech back in the day, Yamaha did a pretty good job of it.
50yrs on it ain't such a "shiny object" anymore... but back in the day it was a "cool" feature.

Back around 1983 it happened to me just as you described. Riding my Moto Guzzi V50 on a country road on a moonless night near Warrenton, VA, in a high speed sweeper, I suddenly lost my headlight. No reduced power to high beam, just darkness. Fortunately I was familiar with the road and just held my course as I slowed down and eventually found the rather minimal shoulder where I switched the headlight switch on and off and jiggled the ignition switch which got the lights working again. Next day I removed and disassembled the ignition switch and found all the contacts were corroded. I cleaned them up and everything worked fine ever after. I think I will try to keep my resister on my XS650D if I can figure out it's value and wattage...

 

[Kevin Werner]

Check for 12v at your on/off and Hi/Low switches. If the new bars are painted clean off the area under the ground contact.