Topic: 1977 cb550 k3 headlight wiring

[PeteHart]

Hey All,

Relatively recent new reader of sohc4, first time poster. Finally found something where I can't find a good resource already on this form.

I have a '77 barn find cb550 k3. I have it running well but I am running into strange wiring issues. When a battery is installed I can start the bike, but both the headlights and taillights arent getting any voltage. Here are the things I have tried to trouble shoot the issue:
-I replaced all the fuses, though the ones that were installed still had conductivity when checked with a multimeter
-I checked the headlight and tail light bulbs, all work when jumped to a battery
-I verified that we have voltage after the fuse pannel all the way to the component listed as "off no connections" on the k3 wiring schematic that can be found at http://manuals.sohc4.net/cb550/technical_reference/WD550C.jpg . I am unsure how to track the power past this component to attempt to discover where it being lost before making it up the wiring harness to the headlight.
-When measuring the voltage at the headlight, I find the green lead is grounded, blue and white are the positives for each coil (I think). I get a voltage differencial of 0v between blue and green and about 1v between white and green. this doesnt change when the 'high/low' selector on the grip is changed.
-I have found the ground lead for the rear lights, but I cant get any of the other wires to go hot in any state.
-When I track the white and blue leads from the headlight they appear to both lead into the grip control, but I dont want to cause more damage than good breaking this down to track them. Could a faulty grip control cause this issue?

The bike was partially disassembled when I found it, all the turn signals were missing.I haven't yet ordered replacements. could this be part of the issue?

One weird observation - When I swap from low beams to high beams with a led headlight, the headlight will flash on for just a second. this happens for both going from to low to high, and from high to low. It appears to be the low beam bulbs, but its really hard to catch.

I'm kinda at a loss for what my next step should be to diagnose this issue. any ideas?

Thanks a bunch! Peter

[Deltarider]

Why not use the correct wiring diagram for your specific model? There are three according to the 'area code'. They're found here in p. 182-4 https://www.classiccycles.org/media//DIR_1653304/DIR_1653404/DIR_1653507/ecc6759db0a214d5ffff8825ffffe41e.pdf You can determine what specific model you have by comparing your frame- and enginenumber with those listed in page 4 of the appropiate parts list. http://www.honda4fun.com/pdf_parts_list/pdf_spac500-550/CB500-550_K3-K4.pdf Succes!