Topic: No power to headlight - 1974 CB550 [SOLVED]

[95chris]

Hey everyone,

Looking to get some guidance on what to check next on this issue I'm having on the headlight. Bike is a 1974 CB550 and is a runner.

So far I've confirmed these are in working order:

• Headlight is GOOD. Turns on when connected directly to battery (HI/LO)
• Fuses are not blown (blade type). Voltage is present across all fuses
• ON/OFF switch on RH side looks to be working, gauge/dash lights will illuminate when switched ON and power off when OFF.

It doesn't seem like I'm not getting voltage to the blue and white cables leading up the headlight (unless you count 0.07V...) when switching between both HI & LO positions. The HI beam bulb stays off when HI beam is selected.

One thing I should mention is that recently my starter button no longer worked and the bike would not crank. I found out that the wire leading to the tiny contact plate in the RH switch corroded away from the plate. Re-soldered it and now she turns over when pressed. This is the only major fix I carried out when wiring everything up, maybe it's related somehow? Headlight was working previously up until I went for a start.



I've only just pulled out the LH switch to do quick a check continuity on the blue and white wires and it sounds good. I will be pulling out that bracket on the HI/LO switch to do a bit of cleaning tomorrow.



Any information on what to check next and/or info from your own experiences would be appreciated!

Thanks,
Chris

[flatlander]

as you had the right-hand handle bar switch apart when you soldered the starter button, and you say that the headlight worked before you did that, that's the obvious place to look. maybe something wasn't re-assembled correctly?

don't know what type of switch you have. i have a european type with a sliding switch for no lights - parking lights - running lights.  that's where i'd be looking in my type of handlebar switch.

[newday777]

There is a start button headlight cutout circuit in the start switch and probably have a burnt out connector to the lights there.

[bryanj]

Dont think that one has the starter/lights type button, suggests the on off is faulty

[flatlander]

There is a start button headlight cutout circuit in the start switch and probably have a burnt out connector to the lights there.

yes if it has that auto cutout, that's a very likely candidate.

[Don R]

http://manuals.sohc4.net/cb500/service_manual/HSM500550_11.pdf 
 This diagram is useful as it shows relative location of the wires.

 Page 145 has the 550 diagram.
   Old man Honda has color diagrams that are nice to follow too.
   I print them on two pages and paste them to a piece of cardboard.

[Don R]

http://oldmanhonda.com/MC/WiringDiagrams/CB550.jpg

 It appears the headlight switch is fed with 12V+ black in the headlight bucket, which is hot with the key on, it goes to the headlight on/off switch and comes out brown/white, that feeds the accessory lights, and one wire connected to it turns red/brown. It feeds the 7A fuse in the fuse block which then goes back up front to the dimmer switch. That wire switches power to the blue or white for high or low. All of these colors are in the headlight bucket where a test light with a pointy probe can detect whether power is at each plug-in connection.
 
 

[95chris]

Just wanted to give a big thanks to everyone for helping me out! I was able to figure out the issue...

http://oldmanhonda.com/MC/WiringDiagrams/CB550.jpg

 It appears the headlight switch is fed with 12V+ black in the headlight bucket, which is hot with the key on, it goes to the headlight on/off switch and comes out brown/white, that feeds the accessory lights, and one wire connected to it turns red/brown. It feeds the 7A fuse in the fuse block which then goes back up front to the dimmer switch. That wire switches power to the blue or white for high or low. All of these colors are in the headlight bucket where a test light with a pointy probe can detect whether power is at each plug-in connection.
 
 

That was the ticket. Unsurprising to me, it was a wiring error.  I had the Brown/Red wire from the LH switch going to the Green/Red "Y" junction meant for the RH switch and clutch switch. Looks like I missed the single Brown/Red wiring coming out of the main harness. I blame my red/green colour blindness and colour fade.

I guess it's customary to post our bikes or whatever project we're working on, also it would be an update to my first post to the site. Last image the bikes current state, easier to do hookups without a fairing on. 



Cheers!
Chris

[flatlander]

yes, always good to see the bike 
nice 550. what's your plan with it?