1. Go to Myron's mopeds and locate the correct wiring diagram and download it.
2.im assuming the moped is a typical 6v moped. Hpi puts out 12 v ac. So all circuits need to have 12 v bulbs
3. Look at the wiring diagram and figure out if the other end ignition coil ( under the flywheel coil)!on the original was grounded to frame directly or if it was used for something such as the brake light.
4. If some other use such as brake light then that part of the bike requires a re wire. That's where ya gotta use your noggin. Often the brake switch on the handlebars need to be changed and the power needs to be tapped off the light coil. And the way it grounds needs to be changed.
5. This can also be an opportunity to rectify and volt regulate to DC and use leds..many many posts concerning how this can be done abound.
Feel free to PM me AFTER YOU STUDY THE WIRING DIAGRAM. I have my ways of doing a 12-v DC conversion that others don't agree with. Mine def work. I have the HPI mini on three hobbits and my magnum.