Testing a headlight switch 57SA

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Aug 23, 2017
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Hey all,

What's the best way to test a 57SA headlight switch? I've got it off the bike and here on my kitchen table. Should there be continuity between tabs with the switch in one position and not in the other? I'm not getting any continuity between any of the tabs with the switch in either position, but still being new to world of electricity, I'm not totally sure if this is significant or not.

I connected my battery for the first time today after replacing the main wiring harness and cleaning up (and in some cases repainting) most of the electrical components. I am pleased and proud to report that almost everything seems to be working beautifully :)!! And that is largely due to help from the knowledgeable, kind and patient folks of Access Norton. I've really been learning a lot, and have been loving every minute of it. It was amazing to see the warning light come on for the first time since I've had the bike, and to hear the horn for the first time, to see that I've got spark, and that I'm not blowing fuses :). Today is a good day.

The one area I didn't mess with when I was replacing the wiring was the headlight. I opened it up and things didn't look too bad so I was (and am still) hoping to get away without buying a headlight harness. Anyway, the pilot light is working great, but the main headlight isn't coming on. No change with the switch in either position, and right hand switch and bottom button have no effect. This is all with the main switch in the 4th position (i.e. all systems go). I pulled out the bulb, and confirmed that it's good. I tested continuity for most of the wires in the headlight harness and the ones I checked were all good. I noticed that there is a good bit of corrosion around the metal piece that presses down against the main bulb seat and provides the ground. That could possibly be the issue. But the lack of continuity between headlight switch tabs is making me suspicious. Do you folks think this could be it, and if so, is it reasonably easily fixable, or is a new switch required?


Hey again,

I think I might have just figured this out :). I took the switch apart and discovered that the little copper bit that was meant to bridge the connection between the tabs was no longer conducting electricity. I sanded it lightly, put it back together and now I get continuity between the tabs with the switch in one of the two positions as I would have expected. Maybe I'll get a working headlight out of it tomorrow :). I'll lets you know.


Nice going. There aren't many who would take apart a toggle switch.
The switch you reference is relatively common; used on Norton, Triumph and BSA most prominently. I wouldn't be surprised if it was used on many similar period British cars, it has that look.

Whereas I applaud your MacGyver-ness for opening up the old switch and cleaning the offending contact I believe that you are right on the border of false economy, A new switch is inexpensive and would be a better match for your new wiring harness. Keep in mind that any high resistance electrical component will diminish the effectiveness of the "system" it is associated with and will suck-up precious watts from your charging system.

Use your resourcefulness' to make the wires that you didn't get with the new harness, replace all the light bulbs, while replacing/cleaning the sockets they live in. I also recommend that you create and run a system level ground loop that starts at the tail light and makes stops at the battery, engine and headlight, don't be trusting the frame, fenders, nuts/bolts, steering head bearings to conduct electricity with any aplomb.
If it was original Lucas I would repair and use in preference to the Wassell's current offerings.
Fingers crossed for that then! While you're playing around with electrickery, and once you've got your headlamp working, one of my favourite wheezes is to put relays in the dip and main headlamp circuits – it takes the load off the switches, giving them a longer life, and boosts the juice to the bulb, as it can now come direct from the battery/charging circuit – it certainly made my main beam much brighter, and I get a lot of pleasure out of riding after dark! When it's not wet and windy ... A cheap, pretty easy and very satisfying modification IMHO. Good luck anyway!
Thanks folks,

Well, I got the headlight working today, but there are definitely some gremlins on the go in the headlight area of the bike.

Thanks for the thoughts, tips and info - its all super useful, as per usual. It is an original Lucas switch, and I was getting zero resistance between the two tabs while testing it in the kitchen before reinstalling it.

The installation went fine, but I did experience some paranormal activity ;). I'll describe my strange experience and see if anyone has any suggestions.

After buttoning the headlight all back up I connected the battery and gave the lights a go. At first I had nothing at all. The pilot light wasn't even coming on anymore. So I started testing continuity with all the wiring etc. I couldn't find any issues with any of the main light wires, or with the brown/green wires that should have been lighting the pilot bulb. And no issue with the two position switch either. So after some head scratching I started checking for voltage at the ends of the wires where they connect to the main bulb. I was getting well over 12 volts on the the blue/red and the blue/white with the dip switch in the appropriate positions. So I figured it must be with the ground and I spent some time sanding the main bulb seating area and the corresponding metal cap that fits on the back of it. I did this several times and hooked it up with no luck. Finally I grabbed two spare wires, connected one to the ground on the metal cap that goes onto the back of the bulb seat, and the other to the blue/red wire end inside that cap, and touched those to the back of the bulb/housing. At first I got nothing, but after a few seconds the headlight came on, and then when I tried connecting the metal cap to the back of the bulb housing it all lit up beautifully. So I put everything carefully back together with it all still glowing so I would know if it suddenly went out with wires being pushed around etc.

Anyway, I got it all back together again no problem, and then I flicked the dip switch on the handlebar and the main light went out, but I noticed that the pilot light was back on. Flicked the switch back to where it was before and no headlight, but the pilot light stayed on. So I was confused and thought maybe it was something in the handlebar switch. So I turned everything off with the main switch and scratched my head a bit. After a few minutes I turned the main switch back on and the headlight came on again, but this time I could use the dip switch just like the two position headlight switch - one way the main light was on, and the other way just the pilot light.

Anyway, that seems to be basically how the headlight is working at the moment. I also noticed that the green light on the headlight shell is not coming on at all - and I feel like that might be a clue since it's part of the blue/white wiring circuit. I haven't seen that green one on yet. Anyway, I'd love to hear any suggestions folks might have on this.

Thanks again,

Sounds like a possible 'ground' problem.

Does the (BPF?) headlight bulb cap, pilot bulb holder and high beam indicator bulb holder all have a connection to the red headlamp harness return/'ground' wire?
Thanks LAB! All three very well might have a connection to that ground wire. I will need to check. I know there is at least one ground wire connected to the headlamp shell itself.
All three very well might have a connection to that ground wire. I will need to check. I know there is at least one ground wire connected to the headlamp shell itself.

Yes, there should be a red wire connection to the shell (necessary if direction indicators are fitted).

The headlamp and pilot should have 'wire' return connections to harness red as the reflector unit and rim do not make reliable 'grounds'.

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Thanks again LAB. I'll have a look now shortly. That unit is exactly like the one on my bike.
Good morning,

I've had a look and yes, all three have wire return connections to harness red. I put the battery back in and turned the lights on while disconnecting to see what would happen. As I took the lamp away from the shell and disturbed things within the shell the lights went out. A little wiggling would make the pilot light come back on, and I've since found that if I twist the pilot bulb housing a little in a clockwise direction it'll come on and stay on when it is supposed to. I was able to get the main lamp (through the blue/red so I guess in reality the dip beam eh) to light, but when I flick the right handlebar dip switch it went out again, and didn't come back on with the switch put back in the up position. The green shell light still hasn't lit up so far.

The plot thickens...
I was able to get the main lamp (through the blue/red so I guess in reality the dip beam eh) to light, but when I flick the right handlebar dip switch it went out again, and didn't come back on with the switch put back in the up position.

Sounds like it could be a handlebar switch fault then, if you are sure everything is connected correctly and the headlamp switch you repaired is working reliably.

The green shell light still hasn't lit up so far.

It won't light up unless the blue/white (high beam) wire has power.

You could test it by connecting a jumper wire between any white wire and the warning lamp white/blue (ignition on), or (ignition and lights on) jumper from the headlamp feed blue/yellow or pilot bulb brown/blue (or blue, + headlamp switch on)
Thanks LAB,

I've taken the handlebar switch off and here's how it looks inside:

Testing a headlight switch 57SA
Testing a headlight switch 57SA

Any suggestions for cleaning/sorting this thing out? Thanks again,

Just send two more. I hope they work. The level of grossness inside the switch is impressive. I've got it apart here now and am getting ready to soak the small removable metals items in vinegar, to scrub out the main housing, and to figure out a gentle but thorough way of dealing with the copper and soldered bits in the delicate innards.
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