Front lights not working

[Phil C]

I'm going to have to do a bit of investigating of this, but would be interested in, and thankful for, any thoughts in the meantime. On my 1965 B40F (6 volts) the front lights aren't working. I turned them on this morning (without the engine running) and got a glimmer of light for just a second and then nothing. The battery can't be completely dead because a) a test light comes on when connected across the battery terminals, and b) the bike starts, so there must be current getting to the coil. When the bike is running the ammeter indicates the battery is charging a bit, esp when the engine is revved.  Any thoughts? Could it be that there is enough in the battery for the coil but not enough for the lights? Thanks in advance for any suggestions. Phil (novice.)

[AWJDThumper]

Your battery is proabably at the end of its useful life. If you fully charge up the battery and then connect a 24W headlight, a good battery should light up the bulb for about 1 hour. If your bulb only stays bright for a small fraction of an hour then that tells you what fraction of the battery's original capacity is left.

[DerekAnderson8]

Do the lights work when engine running? and if so get brighter when engine revved a bit if yes then battery is knacked, it wont take a lot of charge in battery to start if its flat on std ignition system but if running electronic, boyer etc it will also need a decent battery.

regards

derek

[Dabbist]

Maybe going off on a tangent but my trials Cub has  Boyer ignition and doesn't need a battery at all. As long as the alternator is ok, most electronic systems don't.

[JulianS]

If you think your battery is ok then you need to check all the wiring with the circuit diagram and check all connections, separate and clean the bullets and ring connectors and ensure proper earth connections to frame.

[Phil C]

When I turn on the light switch, the engine cuts.  What might that indicate?

Also there was a kind of explosive "puff" sound somewhere down near the battery one time when I was kicking it over today.

The ammeter no longer shows a positive reading when the engine runs.

Any ideas please?

Phil 

[Phil C]

Forgot to mention in my previous post: with the poof sound was a puff of smoke - from somewhere near the battery. Worried me a bit!  Phil (novice.)

[ducati2242]

There should be a fuse off the battery terminal hopefully that was the puff of smoke . When my lights went out there wasa loose connection in the headlight .

[DerekAnderson8]

Maybe going off on a tangent but my trials Cub has  Boyer ignition and doesn't need a battery at all. As long as the alternator is ok, most electronic systems don't.

Not so sure about that 

Electrex world do a self generating ignition that doesn't need a battery and PVL ignition is same. Electrex world also produce a lighting/ignition coil setup.

My A65 has boyer ignition and if less than 12v from battery it wont spark.

Do Boyer Brandsen make a self generating ignition system?

[JulianS]

Going back a few years, my then owned Starfire had Boyer and also a large 2MC capacitor. It would start and run well without a battery.

[Phil C]

Mine is points ignition. The bike starts, but, to recap: 1) when you turn on the lights, they don't come on and the engine immediately cuts out when you turn on the headlight;  2) there was a poof and smoke somewhere near the battery today when I was kicking the engine over;  3) the ammeter now stays about zero, rather than shows a positive reading as before today.  I'm guessing a new battery might be one thing needed.  I don't see a fuse (maybe need to look harder) and I don't think any are shown on the wiring diagram.  Anyway, and ideas regarding the points 1, 2 and 3 above please?  Phil (novice.)

[JulianS]

Back to my earlier point. Check it all.

Smoke is indication of trouble you will only find out what by examining the wiring.

[DerekAnderson8]

Mine is points ignition. The bike starts, but, to recap: 1) when you turn on the lights, they don't come on and the engine immediately cuts out when you turn on the headlight;  2) there was a poof and smoke somewhere near the battery today when I was kicking the engine over;  3) the ammeter now stays about zero, rather than shows a positive reading as before today.  I'm guessing a new battery might be one thing needed.  I don't see a fuse (maybe need to look harder) and I don't think any are shown on the wiring diagram.  Anyway, and ideas regarding the points 1, 2 and 3 above please?  Phil (novice.)

There is a short circuit on the negative side, probably at light switch. Poof and smoke could be wiring nearer battery terminals without seeing it difficult to diagnose.

[Dabbist]

Maybe going off on a tangent but my trials Cub has  Boyer ignition and doesn't need a battery at all. As long as the alternator is ok, most electronic systems don't.

Not so sure about that 

Electrex world do a self generating ignition that doesn't need a battery and PVL ignition is same. Electrex world also produce a lighting/ignition coil setup.

My A65 has boyer ignition and if less than 12v from battery it wont spark.

Do Boyer Brandsen make a self generating ignition system?

I'm pretty certain that Boyer don't do a self generating system. Theirs relies on the output from the alternator. In fact, until fairly recently, if your alternator wasn't too good their system set itself to full advance, which made starting really interesting... and painful! I ended up fitting a little Li-on battery to my Cub, on a horn push, just for starting.
As you say Elextrex do and I'm planning to fit theirs (the one with the lighting generator as well) to my B40.

[Dabbist]

I think Julian S has hit it on the head.  If you have smoke, something has burned out.  Physically check the wiring first of all.  Start where you think the smoke came from and if you can't see anything...

Is anything loose?  I've seen batteries move about and short against the tinware.
Look where wiring passes through anything metal (like the headlight shroud) in case a grommet has worn through and caused a short.
Look where wiring moves, e.g. near the steering head.
Look around any connectors that aren't well insulated. You might see arc strikes on the metal nearby.
As Derekanderson8 says, the light switch is a good candidate, it has moving parts that can become loose.
Also look where wiring can get caught, under the tank is a good one, it can wear there if it's not properly routed.

The lights stopping the engine is often a sign that the bike isn't charging.  If the battery's getting low (which yours obviously has) then it can't supply the coil and the lights as well.

Thinking about it, if you stick all that together then it looks like something either shorted and died or just gave up and stopped the bike charging.  Check out your rectifier/zener diode (I don't know what your bike has) as that could make smoke and stop it charging.