Topic: CB750F2 Lights stopped working suddenly

[vitjakes]

Dear users,

I've recently picked up a 1978 barnfind CB 750 F2 and dug into refreshing all the necessary parts to fire her up again. After installing a brand new battery and replacing all the fuses, I turned the ignition on to check if everything works. At first, it all seemed fine. All the dummy lights showed up, the horn worked as did all the lights, brake lights and turn signals. I then tried to switch to high beam from low beam and this worked for me too. It was only until I pushed the start button to see if the starter motor works (which it did just fine) that half of the system went down. All that remains working now are the dummy lights and starter. All fuses are ok, I even checked voltage on all six terminals showing reasonable 12,5 volts so the current is flowing through them. Is it possible that there's some sort of battery-saving feature that wouldn't allow for the light components to work before the bike is started? Can some one please chime in? Thank you kindly!

[ekpent]

 I believe that the F bikes have a built in circuit in the starter button loop that automatically cuts power to the headlight when it is pressed to save energy from the battery while starting the bike. You probably have a malfunction in the button assembly causing that. Same thing went wonky for me on a 1976 F bike.  Just for fun keep manipulating the button,pressing on off etc. to see if the headlight all of a sudden comes back on.

[vitjakes]

Thank you. I had a suspicion there could be some kind of this sorcery. Is it fixable or, possibly, is the malfunction visible/detectable with the eye?

[TwoTired]

Thank you. I had a suspicion there could be some kind of this sorcery. Is it fixable or, possibly, is the malfunction visible/detectable with the eye?

Inside the bar control and behind the start button, is a spring loaded rocker switch.  Center fulcrum connection is Power (Black), and the rocker bridges to the headlight power post (Black/Red) or the Starter Solenoid post (Yell/Red).  The spring holds it in the Headlight power position, unless the button is pressed.

The switch housing plastic has a tendency to crumble when the solvent used in the plastic manufacturing process dries out.  Or, brake fluid leaking from the master cylinder weeps into the bar control housing and attacks the plastic.  When the plastic crumbles, the metal bits inside lose proper orientation, and the rocker connections become iffy.

I have repaired some crumbly switch housings, with cleaning solvents and glue.  It is a fiddly process, some akin to repairing mechanical watches, and Assembling a three masted schooner inside a bottle.  Optical magnification helps, as does a steady hand.

I think a new plastic housing should be a better option.  I bought some from shapeways, but haven't had time to use it in a repair yet.

http://forums.sohc4.net/index.php/topic,163170.msg1931747.html#msg1931747

Cheers,

[vitjakes]

Thank you for a thorough explanation, but mine didn't seem to have this feature. What I, stupid me, found out, was a disconnected ground around the coils as the wiring was a DIY nightmare... All is well!