Headlight is making me mad!!!

Ongoing issue with the headlight on my 73 750. I usually leave the toggle switch in the on position, so that key on/off gives me the headlight every time. The issue I keep having and trying to track down, is sometimes when I turn on the key and star the bike, the headlight doesn't come on, and the green hi beam light is lit. If I give a little tap to the front of the headlight, green light goes out, headlight comes on. Problem won't come back till maybe the next time I turn the key off and start up again (but not always) I've looked around and around in there for something loose. One issue is recreating the problem for trouble shooting. If it happens, the second i touch the headlight to loosen the screw and pull it apart, it rights itself. One thing I tried was loosing the "wrap around" type bullet connectors that were on the ground for the bulb, and to the shell, and soldered on bullets to replace them. Seemed to do the trick for a few days, then the gremlin came right back again. Anyone have any suggestions where I might look around to solve this?

Just a suggestion, but anytime you see a problem like this, try running an earth lead directly back to the battery.

Best used only for troubleshooting, since it may or may not be fused, depending on how your electrics are...
If your existing earth is going through your steering bearings, maybe waggling the handlebars will fix it !?

I run my headlamps through 2 relays that are fed by a by a heavier negative cable through a fuse, and a return [ heavier ] positive cable direct from the battery. I would suggest cleaning the contacts on your switches [ dip and master switch on the headlamp ] as well. A few times I have been out that switch on the headlamp has given a hiccup, but has been corrected by madly switching the switch back and forward. My switch is original as far as I can tell, and it is probably suffering from old age. At least running your lamp through relays will give you brighter lights.
Your problem could also be a broken contact somewhere.

kevbo82 said:

The issue I keep having and trying to track down, is sometimes when I turn on the key and star the bike, the headlight doesn't come on, and the green hi beam light is lit. If I give a little tap to the front of the headlight, green light goes out, headlight comes on.

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Sounds like the headlamp bulb ground wiring or bulb holder has an intermittent connection somewhere? If the main bulb loses its connection to ground, then the [Edit] low (dip) beam bulb feed current can pass across both main bulb filaments and use the high beam warning lamp as its 'escape' path to ground. The warning lamp lights up, but the main bulb doesn't (or at least it may glow very dimly) because the warning bulb will then be acting as a resistor.

kevbo82 said:

One thing I tried was loosing the "wrap around" type bullet connectors that were on the ground for the bulb, and to the shell, and soldered on bullets to replace them. Seemed to do the trick for a few days, then the gremlin came right back again. Anyone have any suggestions where I might look around to solve this?

Click to expand...

Does the main bulb 'ground' have a direct connection to the red return harness wiring, or only a ground connection to the headlamp shell?
I think perhaps the reason for the shell ground point is often misunderstood, as it shouldn't be regarded as the 'ground' for the headlamp, but as a connection from the shell to the harness return (red) wiring for the front direction indicators/blinkers which would otherwise have to ground via the headlamp brackets (which have O-rings at both ends so consequently may not make particularly good electrical contact with the yokes/forks) and the steering head bearings.
Obviously it would not be an ideal situation if the headlamp circuit has to return through the headlamp brackets and steering head bearings,which is why the headlamp needs to be connected directly to the harness return (red) wiring.

L.A.B. said:

Sounds like the headlamp bulb ground wiring or bulb holder has an intermittent connection somewhere? If the main bulb loses its connection to ground, then the [Edit] low (dip) beam bulb feed current can pass across both main bulb filaments and use the high beam warning lamp as its 'escape' path to ground. The warning lamp lights up, but the main bulb doesn't (or at least it may glow very dimly) because the warning bulb will then be acting as a resistor.

Click to expand...

Good info! Got my brain working in the right direction I think.

L.A.B. said:

Does the main bulb 'ground' have a direct connection to the red return harness wiring, or only a ground connection to the headlamp shell?
I think perhaps the reason for the shell ground point is often misunderstood, as it shouldn't be regarded as the 'ground' for the headlamp, but as a connection from the shell to the harness return (red) wiring for the front direction indicators/blinkers which would otherwise have to ground via the headlamp brackets (which have O-rings at both ends so consequently may not make particularly good electrical contact with the yokes/forks) and the steering head bearings.
Obviously it would not be an ideal situation if the headlamp circuit has to return through the headlamp brackets and steering head bearings,which is why the headlamp needs to be connected directly to the harness return (red) wiring.

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Yes, going from memory here, It was a double snap connector that has the ground coming in from the harness, goes out to the shell, another to the bulb, and 3rd to the green hi beam bulb. I figured since there was a ground from the harness and the turn signals only had one wire that the shell was grounded from them, and they work just fine, but i replaced that connection just in case. The snap connector is brand new from britishwiring.com as well (i replaced all of them on the bike) I did also suspect the what looks to be original toggle like someone suggested, but nothing I do to that either causes or remedies the problem, so I don't think it's that. I'm going to look at the holder for the bulb now as my main suspect. Thanks guys

I'm also thinking the fault could be within the actual bulb itself, so maybe try another headlamp bulb if you have one?

L.A.B. said:

I'm also thinking the fault could be within the actual bulb itself, so maybe try another headlamp bulb if you have one?

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I believe my dad had a couple original lucas bulbs still in their boxes in his garage, have to take a look.

Right on queue! Turned the key on this morning and green light comes on, I was finally able to VERY SLOWLY open the headlight up and keep it in that state. I pushed down on the back of the holder and the green light went out, headlight came on. Released pressure and it went back to headlight off green light on. So definitely in the hold and/or bulb. I'll clean up the connections and try a new bulb.

Try the red wire pushpin into the wound tin groundclip in the Headlight shell. Mine was loose and lost it's springy strength and the little green indicator light would act up periodically too. :wink: