QT50 HPI wiring problem

In the process of resurrecting a 1979 QT50 I found that the charge coil was dead which probably explains why the previous owner parked it many years ago. With the very limited supply of NOS charge coils I decided to bite the bullet and go for a HPI ignition. Installation of the new ignition went well and it starts mostly first kick and runs well. Here's my problem. Can anyone offer advice as to how to wire the HPI system into the stock wiring harness so as to restore all the original functions i.e.: lights, turn indicators, brake light, ignition switch and horn.

Any help will be greatly appreciated.


Re: QT50 HPI wiring problem

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.

Re: QT50 HPI wiring problem

Re: QT50 HPI wiring problem

Jack Rutherford /

Yellow lead off the hpi stator to regulator to blue wire on Qt50. You need to buy a regulator or maybe use the qt regulator if you have a later model qt.

Re: QT50 HPI wiring problem

There's more to it than just running the yellow lead from the stator to the blue lead in the stock wiring harness. All that does is supply current to the instrument cluster. Tail light, head light or turn signals all not working. The wiring diagram available online is for the later production bikes that came with a voltage regulator. My bike doesn't have a regulator but I did locate an owners manual my bike that shows no regulator in the wiring diagram. Someone out there must know which wires go where to restore all the original functions including a battery.

Re: QT50 HPI wiring problem

Did you look at Myron's mopeds. I expect the wiring diagram is there. Super fun website..great guy.

Re: QT50 HPI wiring problem

Jack Rutherford /

You’ll need to buy a regulator then.


Here’s the instructions. Perhaps you got into more than was necessary. But the only connection from hpi to stock wiring is hpi yellow to qt blue unless you want to wire in the hpi kill wire to the stock harness.

Maybe I’m missing something but you’d instructions on their kill wire seem like there should be more. (edited)

Re: QT50 HPI wiring problem


Start here. Study and understand how stock is done. Carefully reroute what's needed. There is no other way.

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