Lights on / Lights off.... the lights keep dying then recovering.

[Barrieh]

BSA M33 Plunger - 1955 - New Lucas Wiring Loom - diagram followed religiously, new battery 6v positive earth, refurbed, Lucas Magdyno, new solid state rectifier.

Lights switch off / off from the battery, all good.
Run the bike, get it night are warm running for about 20 min, all good... except the lights have died....
Leave the bike for 30 min or more to cool down... lights come back on.

Its a standard off the shop floor 6v positive earthed system, the magdyno was professionally rebuilt... I am so confused... any ideas?

Any ideas warmly welcomed!
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[Rog1]

You most likely have a bad contact somewhere, creating a resistance. It gets warm under use, the metal changes shape, the contact opens, and out go the lights. Leave it all to cool down, the metal returns to its original form, and the lights come back on.

When you have a contact that's bad because it has a resistance, the contact's temperature will go up under use, which makes the resistance go up, which makes the contact's temperature go up, which...

It might be a badly soldered joint.

[Barrieh]

That sounds most likely...agreed.

I have fitted a single 6V 4amp Lucas sealed battery I got from Feked.com.

Does it need to have a greater capacity e.g. am I overloading it, causing it to get too hot? I wasn't sure on the battery capacity requirements for the bike.

I will look through my wiring tonight but I cant think of anywhere it could be having resistance, as you know its a very simple system? Mystery or what!

[JulianS]

I suggest test the electrics in sections.

Check all the connectors in the loom are properly connected to the cables and ensure the whole system is properly earthed

Test the dynamo output, before the regulator, useful information on this site;

https://www.matchlessclueless.com/electrical/lucas/testing-lucas-dynamo/

Then test the output after the regulator, there may be some information for this supplied with it. Some regulators have a better reputation than others. For me the best is the DVR2.

[Rog1]

That sounds most likely...agreed.

I have fitted a single 6V 4amp Lucas sealed battery I got from Feked.com.

Does it need to have a greater capacity e.g. am I overloading it, causing it to get too hot? I wasn't sure on the battery capacity requirements for the bike.

I will look through my wiring tonight but I cant think of anywhere it could be having resistance, as you know its a very simple system? Mystery or what!

If the bike is charging then you are not overloading the battery. With the lights on the bike will not be charging until you are moving at a reasonable speed for the gear you are in; it's only a 60w dynamo after all! But if the bike is not charging the lights would get dimmer and dimmer until you couldn't see that they were on, and that might well happen in 20 minutes. A 30 minute rest would allow the battery to recover but not fully; you wouldn't get another 20 minutes of lights out of it.

Check the contacts in the light switch. Mine (also on an M33) was pretty horrible; the road dirt had got to it. Did you have this problem before you did all the electrical work?

[Barrieh]

Its a brand new restoration... the bike was a complete mess... came back from Burma in 1997 having been on the road from 1955. Its been a lot of work/fun.

The running in process is hampered by this lights failure which is driving me nuts! Its a new Lucas wiring loom part number 865493 - BSA B/M group 1946 to 1955 Rigid / Plunger Frame. The diagram is quite clear and I have followed this through very carefully.

I am now wondering if the dynamo is actually working or I have missing something. All lights work, horn, break switch, etc all good... but perhaps its not charging....

I will have read through the Matchless webpage and try and see if it charges.

Hamish

[Barrieh]

I meant to say that the MagDyno were fully rebuilt to a new standard... so I am confused

Hamish

[Barrieh]

Hi,

One question I do have is this wiring diagram for + or - earth... I am trying to workout if I have the right regulator fitted.

The loom is basically the same as the diagram attached. Its a standard Lucas magdyno as fitted to the BSA in 1955.

Any suggestions?

Hamish

[Derek996]

That diagram is for a negative earth, same as my 1949 B32. You can see that the positive black/yellow wire from the battery goes to the ammeter and the black wire from the battery negative goes to frame ground.

[Barrieh]

Thanks Derek. I am a little confused - my fault for not reading up enough on this subject.

I have a Lucas E3LM Dynamo fitted  60w - I am assuming for +,  so why have Lucas created wiring for negative earthed frame? Surely the wiring should be + earthed?

I am assuming you have the same setup. I have kept everything 6V but what regulator would I then need? I went down the solid state route but I suspect I have probably damaged this as it was a + 6 regulator.

Thanks
Hamish

[Barrieh]

Spoke with Kidderminster BSA who have set me on the right path. They suggested keeping it + despite the loom being set for - because there were issues with the - Control box/regulator they supply. Fine by me.

1. Setting polarisation of Dynamo - Set Dynamo to (+) flow by putting a wire from (-) terminal of 6V battery and swiping it against the Dynamo F terminal.
2.  Reverse the battery around so its + battery to - on the loom etc.
3. Reverse the Ammeter around.
4. Pop the new regulator in following their recommended diagram - to be sent to me.

I have to be honest that this is all new to me but I would like to thank you for all the help.

Hamish

[JulianS]

BSA changed from using negative earth to using positive earth in the early 1950s. Certainly the 1953 season models and later were positive earth, using different colour coding on the wiring than the earlier loom.

I see that these new "LUCAS" looms are being sold covering the all 1946-55 M models?

[Derek996]

If it helps, here is the -ve earth diagram for pre '53 bikes and the +ve earth diagram for '53 on.

[Mike40M]

The 60W E3L don't give much at low revs, so it might be that your battery is draining with lights on. Especially with a 4Ah battery, which I think is less than the original. For a Norton WD16H which had been upgraded with an EL3 from the 40W E3, I fitted LED lamps some 5 years ago. Got no battery drain with lamps on at moderate revs. Back then LED lamp beam pattern was poor, but I'm told that there are LEDs with a decent beam pattern now.