This might have some information that's useful. I can tell you-- hooking up something to the moped electrical is a delicate matter and won't provide heavy amps for anything needing real juice-- and if you overpull the system things are going to heat up and cook. Plus the wiring isn't meant to carry the load-- so if you've got resistance in the line it'll heat up and cause more resistance.
an example would be connecting a car amp to a large battery using braided stereo coil wire instead of inline electrical wire.... use a thin wire and between the current's pull and the wrong wire confusing electron flow....those wires will get red hot and act like toaster elements. If they don't actually melt into total degradation the amp or motor might cook too. a lot of electrical stuff depends on the proper temperature to run right... to much or too little current can be pretty stressful on components.
P.S. the motor on a tape deck can't handle the shock of the road. use an amp only and run a digital rca inline source to it.
"Here's a few posts on the subject": https://www.mopedarmy.com/forums/discuss/1/33822/33822/