Scooterotica

I've just converted my J-range to Varitronic (no battery, 12V AC). It starts OK, so it seems that the ignition side is OK (I haven't set the timing yet).

However, I could do with a little help with the wiring. I used a combination of the instructions from Cam Lam, together with the diagram that comes with the kit, which they say is correct to do. The instructions say to join the loom's pink, brown and purple wires together, and join them to the yellow output wire from the stator. So far so good, the lights and brake light work fine.

This left me with a spare orange wire from the loom at the rear junction box. I've worked out that this is for the horn, as without it connected, the horn doesn't work. When I connect it to the pink/brown/purple bunch, the horn works when the button is pressed, but the lights cut out. I don't mean that the lights go dim due to the horn taking some of the available current, I mean they cut out completely.

I've looked at the wires for the last hour, but I'm starting to go cross-eyed.

Help

This is the original wiring diagram showing the orange wire feeding the horn. It seems that it's a dedicated 6V supply just for the horn.

I've joined this orange wire with the other power supply wires (brown, pink and purple), but when the horn button is pressed, the horn sounds but the lights (headlamp, speedo, rear, brake) cut out completely.

The varitronic has crap power output at low revs , have you tried the horn with plenty of revs? LED rear bulbs may help .

Yep, pressing the horn cuts all the lights at all revs. I've already got an LED stop/tail lamp.

Check the h/bar switch out as it sounds like something is shorting out.

It's definitely to do with me joining the orange wire to the others at the rear junction box. Looking at the diagram, the orange needs a direct feed, without being connected to the other feeds. It definitely worked before I fitted the Varitronic, and the switch hasn't been touched.

Oh well, bank holiday tomorrow, time to get back in the garage

Try running a wire from a headset live wire(brown) down to the horn instead of using the orange and see what happens. I run my horn from a small battery cuz it was useless at MOT time.

Thanks, I'll investigate further tomorrow. However, since the problem arises when the horn wire is joined to the combined brown/pink/purple wires at the rear junction box, I would've thought that the same thing would happen if I tap into one of those same wires in the headset.

As usual, the supplied instructions are useless, not making any mention of the orange horn wire, despite it appearing on all the J-range models that the kit was supposedly designed for

Have you changed the horn for a 12V one, I would replace the horn with a 12v lamp and try it if it all works your horn is shorting out. The only reason you have multiple feeds is that the old stator used multiple coils you should be fine connecting them together or use a small battery.

No, the horn is the original 6v one. I read somewhere that the horn would be fine for 12v, as long as it's still AC. It sounds fine (well, as fine as Lambretta horns ever are!).

I'll try substituting a lamp tomorrow to see what happens.

I know the horn button switches the earth, but does pressing it connect or disconnect it? I'm guessing that it's not short-circuiting the lights, as they come back on again once the button's released. Presumably if it was a dead short, they would blow immediately?