Electrical anomoly

Yes, I know it’s a 70’s Italian bike, but this one is a bit weird.
My LM1 replica, keep blowing bulbs, I’ve checked the operation of the regulator, and it never goes above 13.5Volts, during normal running.

However, despite it being back to NBS for investigation, all they did was put new bulbs in.

I had the bike out of the garage over the weekend for further cleaning and rather than try and push it up my drive, I started it, warmed it up and rode it in.
I switched it off with the ignition key, and the lights went super bright, and it popped the headlamp bulb, and the speedo back light.

I replaced both (again), and restarted the bike, checked the volts etc, and all was good. This time however, I stopped the engine with the kill switch, and no voltage spike, no blown bulbs.

Any idea why this would make a difference ?

Voltage regulator?

Weird that it only spikes when switching off via the key, not when running / revving, or switching off via the kill switch.

Did the lights go bright as it was switched off or is it a standard switch with off - side lights - on operation ?
Were the lights switched on when you turned the ignition off or did they suddenly light up with the lights ‘off’ ?

If it didn’t blow with the ignition circuit off via the stop switch then I’d suggest this infers high current from the alternator with the engine running. If you have ruled out the regulator and rectifier then it suggests a poor earth connection causing high current.

If it is always the same bulbs blowing then you have a place to start.
As a first step I’d check all the earth connections and then look for a short if the lights were switched off.

Have you considered a potentially faulty ignition switch ? The headlight shouldn’t have any connection with the switch in the ‘park’ position.

I hope this helps.



Engine was running, and the lights are permanently on. So, as the ignition key was turned, the headlamp and tacho light went super bright, and popped, due to over volts.

Note, this doesn’t happen if the engine is stopped via the kill switch.

Agree with the last comments, if the reg/rectifier has been eliminated then it’s likely you have a short circuit (earth) somewhere and one of the first places to look from the symptoms you describe is the ignition switch. Possibly one of the connections in there is causing the fault, the voltage seems in the right ball park, usually on any 12 volt system the supply with the engine running can be up to around 14.5 volts and it fluctuates with engine revs to some degree.
I would remove the ignition switch and possibly use “jumps” to start the engine and lights (make sure they are clear of frame/tank etc) then remove them to turn off the engine and see if the fault is still there.
Incidentally its a little bit strange that the bulbs blow and not the fuse so maybe not an earth fault after all ?? but still worth eliminating the ignition switch, electrical gremlins are usually identified by a process of elimination.


It’s a voltage spike (hence the super bright flash before it blows the bulb) rather than a massive current draw.

What other electrical mods has it got? Anything with a big capacitor? Non-stock rectifier/regulator? I’m struggling to see where the extra Volts comes from. Normally the stock alternator doesn’t even make charging Volts at idle, let alone any kind of a surge.

Just had a thought, what are the chances the regulator is looking at battery Voltage, which “disappears” when key is turned off, hence it over compensates and turns the wick right up? Still needs the alternator to deliver the excess tho. If you were revving at 6,000 rpm when you turned off that would kinda make more sense…

PS: has it got a non-stock alternator, e.g. like the Ducati type, with no rotor winding?

I’ve not gone into it (yet) but have referred it back to the vendor (Muzzi Moto) and the builder (Nigel Billingsley). They have so far not responded.

I’ve just been out and retested the charging system, and the regulator isn’t regulating ! As the revs rise the volts rise above 15V at about 3,000rpm, so at least we know where we are looking.

I’ve unbolted it from the frame and sent Nigel a photo so that he can recognise it and hopefully supply a replacement.
Fingers crossed !

is is the one thats on the bike now.
REGrec m.jpg

And the alternator, so I assume that I have the combined reg / rec bolted to the frame ?
alternator m.jpg

That’s no regulator that I recognise! :open_mouth:

Thats the back face, that goes against the frame, the “normal” fluted side is away from the camera.

The red insulators to the spade terminals indicate to me that this has been altered and is no longer standard.

It is an aftermarket one that has been put on as combined Reg/ rectifier. The backplate on the 2nd photo shows where one part USED to be.

Muzzi / NBS are sourcing a replacement, but nothing in the post today, so looks like another week without the bike.

Still doesn’t help me! :astonished: (Cue sound effect for ‘going over my head’). Still all Greek.

What Chris said.

If you look at the soldering of the three yellow wires to the circuit board the solder has got too hot and melted the yellow wire insulation and has burnt the circuit board. There is no telling what damage it has done to the components on the board or the printed connections between them. I would get the whole reg/rect replaced by whoever you got it from and try and get one with wires attached in a factory or by a competent assembler/electrician.

replacement unit arriving from Gutsibits tomorrow, so on it will go !