Topic: 1977 CB550 -- Headlight issue.

[Crapachi]

I am experiencing intermittent headlight failure (meaning mostly not working), which sucks, since it's unlawful to ride a motorcycle without a working headlight in the state of Washington.

After subbing in a brand new battery, examining the ignition switch, fusebox, and various connectors, I'm perplexed by this following results:

On the headlight lead wire I am able to use a voltmeter to detect voltage coming from the headlight selector switch.  However, with socket connected to this lead and then grounded to frame, the light will not come on.

I also get the same voltage reading on a nearby wire associated with a taillight/accessory circuit.  When I connect the socket to this wire, and ground to frame the exact same way, the light comes on nice and bright.

I'm curious what this may possibly indicate.  I've tried backtracking along the headlight circuit and it has only lead to more confusion.

Knowing very little about automotive electronics my best guess is that there is a loose/corroded connection somewhere up the line on the headlight circuit that is giving ample enough resistance to kill off the wattage or something.  Does that even make sense?

Thank you!
- D.

[TwoTired]

The 77 cb550 headlight power is routed to through the stater button.  When pressed, the headlight is disconnected, allowing higher voltage to exist at the coils, so they can provide higher spark voltage during start operations.

The plastic housing inside the bar control does not withstand brake fluid that can leak from the master cylinder nearby.  When the plastic disintegrates, either the starter or the headlight or both cease to function properly from the button press/release.

Starter button failure is a common occurance for these old bikes.  Besides OEM, I know of no common replacement for the switch.


Cheers,

[05c50]

It is possible to show battery voltage on a volt meter,but not have enough amperage to light the headlight. Check for good connections back to fuse box. Brown wire (Hi),white (low) to dimmer switch and black/yellow to fuse box. Dirty connectons could cause excessive resistance.

[Crapachi]

Outstanding.  I appreciate the quick responses, guys.  Thanks!