magneto to charge a battery

[Hero999]

Clearly the alternator isn't designed to charge the battery or power the 55W lamp.

I doubt the 55W lamp uses a chassis return as it's an after market add-on.

If it's possible then use a fullwave rectifier, if not then go for the halfwave.

 

[Nigel Goodwin]

I doubt the 55W lamp uses a chassis return as it's an after market add-on.

The OP said:

you do have to ground the bulb to the engine though.