Prince of Darkness

Hi all, Im hoping some one can help.
I have a 73 850, with no light/horn at all working, but it does run ok apart from not ideling when using back brake, in other words it cuts out when blinker switch or tail light is pressed, so there is a power drew from the battery but no light.
I have gone over all the wiring and cant find any lose out of place wires,all bolbs are ok battery is in good condition, has had a new wiring loom last couple of years.
I'm hoping someone has had similier problems and can point me in the right direction.

thanks joe

Once my norton had a short, and blew a fuse. I came up to a light and hit the rear brake, and the engine stopped. Could your capacitor be taking over and not having enough juice to honk the horn or light? Check your fuses.

What you have described Joe sounds as if the electrical system is running off the alternator output and not off the battery, so (as NateC has pointed out) could be a blown fuse, a break in the wiring or a loose/wrong connection?

With the ignition switched ON but with the engine stopped what lights work (ignition warning?/indicator blinkers?/brake light)?

No, first thing I checked was the fuse

So does everything work with the ignition switched on but engine not running?

With the ignition switched ON but with the engine stopped what lights work (ignition warning?/indicator blinkers?/brake light)?


no lights at all are working when ignition is onin both positions

With the ignition switched ON but with the engine stopped what lights work (ignition warning?/indicator blinkers?/brake light)?

Click to expand...

no lights at all are working when ignition is on in both positions

Does that include the headlamp?

When you say "no light/horn" in your first post is that just the headlight (both high and low beams) that does not work?

joe850 said:

no lights at all are working when ignition is on in both positions

Click to expand...

OK so the lights *do not* work with the ignition on.

So *first* check for Voltage on the brown/blue wire at the ignition switch terminal (with a meter or a 12V bulb).

When you say "no light/horn" in your first post is that just the headlight (both high and low beams) that does not work?

no lights work on the bike at all.

Click to expand...

Ok Thanks L.A.B. for helping out, I did test the brown & blue wire, with a meter & a bolb it checks out ok,I tested all postions on the switch, its getting voltage.
when I was testing things on just the ignision on I had the blinker switch on the on positon I could here the flasher relay ticking but no light on blinkers.
Does this mean the the rectifier, the zenor diode, and the 2MC capacitor, and the control switch are working ok?

joe850 said:

Does this mean the the rectifier, the zenor diode, and the 2MC capacitor, and the control switch are working ok?

Click to expand...

I could not really say for sure if the charging system is working correctly or not, you could start up and check if there's a slight increase in battery voltage with a meter as the engine is revved?

I did test the brown & blue wire, with a meter & a bolb it checks out ok,I tested all postions on the switch, its getting voltage.

Click to expand...

Well, that's not what I would have expected, but anyway, the switch would seem to be working at the ignition position if power is getting to the flasher relay (and you have said that the bike runs) the relay should be connected to a white wire from the '2' terminal on the ignition switch (ign. on position), that same white wire should connect to the brake light switch, so I suggest checking the circuit along this white wire right to the brake light and its earth/ground connection, and do the same for the flasher circuit?

The other white from the ign.sw 2 terminal is the ignition circuit wire which would appear to be working correctly at least?

With the switch set to ign. and lights, do the same volt check along the blue/yellow from ign.sw. terminal 4, this wire should go to the lighting switch, then a blue wire to the handlebar switch and then the high/low wires (blue/white and blue/red) from the switch to the headlamp bulb
(and check all earth/ground connections back to the battery).

(And of course check that all the bulbs actually work)

Hi L.A.B , I did manage to trace it back the very low battery output, I put the battery charger on the battery and started playing with the switch and got some light out of it.
when it first happened I put the charge on the battery to see if the battery chargers lights showed a full battery supply and it did, making me think the battery was fully charged, its less than 1 year old, any way I'm just happy to find the problem.
Thanks for help L.A.B.

cheers Joe.