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Just finished a Series 3 Tv175 renovation. Everything seemed okay but it has developed an electrical problem. Engine starts and runs fine with no light on and with sidelights on. Put the key into the headlight position and the engine cuts out at low speeds(tick over). If your riding the lights are on and the engine runs until you come to a junction when the engine cuts out. Checked all the wiring through and it seem okay. If you disconnect the BROWN wire on the head light junction the engine runs okay, but obviously on head lights. The brown wire goes back to the stator via the rear junction box. Vehicle is on 6 volts. Any ideas???? Has a coil gone down on the stator????

My first thought is that the flywheel needs re-magnetizing......

Ditto

Shorten your plug gap and try.

Condenser fault.

Flywheel was remagnatised by AF during rebuild. New condensor's been fitted.wonder if the internals on the ignition switch have failed hence the cut off when you put the headlights on will drop a spare in and see what happens.

Have you tried closing the plug gàp anyway, just in case?

Plug gap might make a difference & modern condenser quality is a bit suspect, IMHO. AF Rayspeed sell them very cheaply so worth getting a couple to have in hand & theirs are 'pre-wired' so no danger of overheating when soldering in. You can find out how to test a condenser on YouTube, but I've still had fussy ignitions despite testing them, so even I suggest getting new from the likes of AF R.....

My belief (& practice) is to use non suppressed caps with points ignitions & the fine wire Champion plugs are really good to have in place.

Well boys, I have checked all the wiring connections are correct and the continuity of the wires through the loom. I've check all the earths are good. I've fitted another switch and another regulator. Still cuts out when you turn the key to the headlight position!!!!!!!
Found an old post from 2015 with the same problem and one suggestion was to check the points gap. Why would that have any brearing on the engine that runs great without lights and with the sidelights on???????
Stripped everything down and checked the points gap, correct according to Sticky's, page 29, .35mmto .45mm, set at .40mm.
Dropped the gap down to .30mm and fired her up, runs good, sidelights - runs good, headlights- runs good and nice bright steady lights!!!!!!!!!! How perverse is that????????
Put the Varitronic back on the shelf for now but she has been threatened with 'electronic' if she misbehaves any more!!!!
Don't you just luv Lambretta's??????

Great news !