BSA B40 Headlamp Bulb.

[grahamkeen1]

Hi,
My 1966 B40 has been converted to 12V but still runs a 35/35W headlamp bulb which doesn't illuminated very much.
Has anyone used the higher powered 60/55W versions ? Just wondered if there was a problem with the power being drawn and perhaps 'warming' the wiring harness.
Thanks,
Graham.

[R]

I fitted a Cibie halogen insert 55/60w (is that the right way around ?) to a Commando some years back, and the result was sorta brilliant ( nearly half as much light as the average car !).  Thats still less power than if your 35w high and low were on together, so "warming the wiring" shouldn't be a concern.

You will likely find that it draws more than the alternator is keen to supply though, all things considered, so unless you ride around in the lower gears a lot (around town), the battery state of charge is likely to suffer. I didn't need to ride far at night on said Commando, or I'd have needed to have fitted one of these higher output alternators ??

[mini-me]

You will not"warm" any wires although if you ran a very heavy load via one switch  for a long time the switch will get warm.

for those application thats where relays come into the scheme, but you won't need one.

The standard Lucas  encapsulated alternator will churn out over 110 watts on 12v quite happily, no need to change it.

get yourself one of those 60/55 halogen bulbs it will be more than good enough for your B40, higher wattages are availiable but illegal for road use. [ but by god they make those car drivers with their  blue gas discharge set ups annoyed!!]

[iansoady]

I had a 60/55 on my Commando and the alternator (single phase not 3 phase) was capable of running it and keeping the battery charged even when riding through the night on several ACU/BMF rallies.

It wasn't very bright however and I remember having a car following me and seeing my shadow in my own headlamp beam......

[mini-me]

exactly.
headlamp 60watts
coil 10watts
rear lamp 12 watts

more than enough to spare for charging.

I used to run a 350 AJS with alternator AND magneto so had over a 100 watts to blast my way down dark roads. DFor continental trips I hung one of theose Cibie Oscar lamps on the badge bar, a falsh of that made even french HGV drivers dip their lamps.

 but as with all these things good earths are essential.

[grahamkeen1]

All,
I'll get one ordered.
The 35/35 does indeed seem to have both filaments on for main and only one filament for dip.
I'm more interested in being seen than using them to see

As an add-on question for those with a B40, does your side/parking light stay on when you switch your headlight bulb on as per cars or does it turn off, so really just a parking light ? Mine turns off, so just wondered if this is standard behaviour or whether I have a faulty switch ?

Thank you again,
Graham.

[iansoady]

That's the way it should work. Clever stuff......

[grahamkeen1]

Ok,

So now I am puzzled .

I've read the manual and it appears that the Headlamp unit has been changed and now sports one that has a three spade terminal style bulb like a car rather than the original style of bulb, which I believe is a push and twist old style bulb.

The bulb that came with the bike was a Lucas 35/35W bulb. When you turn the headlights on, one filament lights on dip (dim glow) and when you switch to main, both filaments come on and you get a reasonably bright light.

The bulb I ordered was a 60/55W version (Lucas LLB472). When I fit that, on dip I get one filament lit but it isn't really any brighter that the 35/35W bulb. On main beam, only the second filament lights but gives a bright light.

From the workshop manual diagram, I can't see any resistors that would pull down the 55W dip beam to a 35W sort of output. I guess the main on both is ok due to the fact that on the 35/35W bulb I get two filaments on main c/f with one on the 60/55W version.

Any thoughts, suggestions as what is going on !

Thanks, Graham.

[L.A.B.]

The bulb that came with the bike was a Lucas 35/35W bulb. When you turn the headlights on, one filament lights on dip (dim glow) and when you switch to main, both filaments come on and you get a reasonably bright light.

The bulb I ordered was a 60/55W version (Lucas LLB472). When I fit that, on dip I get one filament lit but it isn't really any brighter that the 35/35W bulb. On main beam, only the second filament lights but gives a bright light.

From the description, it sounds very much like one feed wire and the earth were incorrectly connected to the bulb in both instances.

Both main and dip filaments shouldn't normally light at the same time.

Looking at the H4 bulb plug from the REAR, the LEFT (common) terminal is earth.

[Rex]

Unless the B40 is different to every other 1960s-on  British bike's wiring I've ever known, the main or dip are on or off in conjunction with each other.
Follow the wiring diagrams....a feed to the dip-switch, then two wires exit one to dip filament and one to main filament. The dip switch doesn't have a "feed to both" position, it's one or the other.
{This is assuming that the B40 doesn't have the lights M-D operation built in to one of those crappy rotary switches so beloved of BSA in the 1960s...}

[iansoady]

From the description, it sounds very much like one feed wire and the earth were incorrectly connected to the bulb in both instances.

I agree. It is very common to think that the central one is the earth as that is intuitively "correct" - and that will give you what you are seeing.

TBH those connectors are much better than the old push and twist versions although they can overheat if bulbs with too high a rating are used. Ceramic ones are available.

[grahamkeen1]

Now we are beginning to sort out the problems. Again looking at the plug diagram above and assuming you are behind it, looking forward with the headlight beam, I found that :

• The Common/earth had indeed be connected to the central spade.
• The main beam was connected to the left hand spade.
• The dip beam was connected to the right hand spade.

So completely messed up wiring. To cap it all, one of the connectors from the old harness to the style connector fell apart  . More to report soon !

My Haynes manual has one wiring diagram for 1958-66 B40s but none of the colour codes seem to match the old wires that come from the dip switch or even the earth wire. I also have BSA service sheet 808 that seems to agree with the Haynes manual but not my bike! Has anyone got a B40 diagram from a different source that might help me.

BTW, the new sealed beam unit (not fitted by me) is a real pain as it is a very tight fit in to headlamp housing and tends to push the light switch connector off the switch !

Regards,
Graham.

[mini-me]

standard luca wiring for headlamps is
 blue=main feed to dip switch.
blue/white}
blue/ red  } are the main and dip feeds, it does not really matter which goes to what terminal. Its the actual switch that determines if main is up or down at the lever.

brown/black =horn
earth wire is invariably red/positive on a bike of this era.

I suppose its likely you have some kind of replacement harness, would have been Briitax mostly;possibly Wipac so do not take the Haynes as holy writ.

[grahamkeen1]

Thanks for that, I'll have a good trace through later.

On my B40, the dip switch is combined with the horn push.

The dip switch is on the left hand side of the handlebars and the actual switch can be pushed down to the left so parallel to the bars and pointing to the left side of the bike whilst the other position is pointing upright after a push to the right. Is there a convention as to which is usually dip or main so I can put the spade connectors back to suit.

It is quite surprising how little difference there appears to be between the 35/35W and 55/60W bulbs in terms of perceived brightness

I also have another wire coming from the light switch that has been terminated - however that's an investigation for another day.

Thanks,
Graham.

[iansoady]

I normally connect them so that up is main but it's your choice.