MOPED ARMY

I'm looking at a diagram for an earlier Garelli, so this may not apply, but...

There should be three wires coming from the mag, one goes right to the ignition coil, one goes to the horn and headlight circuits, and one goes to ground through the brake light switches. The brake light itself is in parallel with the switches.

Since the magneto finds it's ground through the brake light switches, I'd check this circuit first by tracing the wire (my diagram says it's blue, but yours may be different) right to the mag and temporarily jumpering it to ground.

What may be happening is that you have a high resistance point in the wiring or, more likely, the switches. When you try to pull more current through the circuit, like when the headlight is turned on, the voltage on the magneto's ground rises. This will cause the bike to run poorly, stall, or not run at all.

Good luck!

Garelli's are have a PAIN IN THE ASS electrical system. First off...

Check the tail light ground. ( attaches TO the taillight, and then leads a wire TO a connector ground. )

Check the engine block ground. It is a connector, screwed onto the 2nd engine block mount. ( near the wire terminal, on the FLYWHEEL side of the bike)

The engine block ground has been an SOB to me. Also unscrew ALL the terminal wires, and check to see if the wires are silvery-looking, and bound together. If so, cut/slice the wire so there is fresh wire, twist that up, and put it back into the terminal. Black wire goes to -Black wire. Blue from taillight, with Blue (flywheel) to the other blue. and Gray to gray, then yellow to yellow. Simple! ;)