Topic: Newbie - Electrical system not working

[78CB750F1]

This is my first post - I have been reading the all of the recent and archived posts over the past few weeks as I am rebuilding the 78 CB750 F1 I recently bought.  It's been a great help but now I'm stuck!

When I picked up the bike it was running but the electric start did not work and it had to be started with the kick starter.  The owner said it was due to a discharged battery.  When running, the headlight and taillight worked, although weakly.  I am in the middle of cleaning and painting the frame and replacing worn out parts, so I had disconnected the headlight, taillight and turn signals and moved the ignition key components from the triple tree to a new mounting point on the side of the frame.  I bought new turn signals and wanted to ensure that everything worked as I continued the rebuild.  I topped up the battery and charged it and re-connected the headlight, taillight, and rear turn signals (connected but not mounted).  Turned the key to "On" and expected the headlight to come on but nothing.  No turn signals or taillight either.

What should I be looking for?  Is it possible that the battery is completely dead despite having charged it?

Thanks for your help.

[mick750F]

   It sounds like you may have a battery problem. If you have no way to test the battery try turning on the the ignition to "on" while the battery is hooked up to the charger. If you then get lights you probably have a bad battery. Do this at a 2 amp charge if possible. The directional lights are grounded through their mounting point so won't work unless installed or provided with a ground to complete the circuit.

   One last thing...If your 750F is a '78 then it's an F3, an important point for some diagnostics. Good luck...

Mike 

[78CB750F1]

Thanks - it sounds like a new battery is in order.

Regarding the model spec - although marked as a '78 it has the wire wheels, silver engine and front forks of the earlier F series so I had assumed it was an F1.  It is a European spec model which may make a difference.  I will check the frame and engine serial numbers...

[TwoTired]

Have you checked fuses?
Do you have a voltmeter or ohmmmeter? Decent DMMs can be had for $10-30 US.
Do you have a wire diagram?

All the F models have a headlight interupter as part of the starter button.  When the brake master cylinder leaks, brake fluid attacks and disintegrates he plastic switch inside.  The can leave the headlight and/or the starter inoperative.

A light bulb filament needs at least two connections to the battery to illuminate.  Ground return is just as important and power.  Dual filament bulb can have three wires and share a ground return.
Cheers,

[78CB750F1]

Thanks for the advice - I am going to test the battery first and replace if required, check the fuses, and then check the grounds on each of the lights.