since re-wiring the brake light would be a pain I am going to try this:
Due to a mysterious problem with my tail light on my 78 Baretta 38 I came up with a work around. This wiring mod enables your brake light to function independent from your kill switch. So here it is.
1. Disconnect the blue wire from the magneto.
2.Ground the blue wire coming out of the magneto to the chassis of the bike. I like to ground this wire on one of the screws holding the coil on to ensure a good ground.
3.On the left hand brake disconnect the wires from the brake light switch.
Solder, crimp, or do whatever you need to connect these wires to each other.
4.You're going to need to get a new switch for the right side brake lever. The switch you already have is a normally open switch that functions the opposite when installed due to the brake lever. What you need to get is a switch that is a normally closed.
5. Run a wire from the black wire on the magneto up to the right hand brake light switch. At this point if you don't have the new switch it will not function correctly.
6. Now connect the black wire to one side of the brake light switch and the blue wire that was already there to the other.
7. Go ahead and cut the gray wire off that is coming out of the kill switch. If you want to go the extra mile you can due the next part but it isn't necessary.
8. Take the yellow wire coming out of the headlight switch and cut it leaving enough excess to run it to the left hand brake light switch.
Connect the other end of the wire just cut to the other side of the switch.
What you are basically doing is intercepting the tail light 6V. What this does for you is when both brake handles are pulled. The tail light will shut off and the brake light will turn on. The reason for opening up the tail light circuit for braking is it puts less current strain on the small wires on the moped.
From the wiki.