Pretty basic wiring on a '72 Prowler. There's a yellow and a black wire coming out of the engine. Run them in some 1/4" black plastic tubing or heat shrink tube up the frame to under the seat. Leave some slack, as the engine will flex. Route and zip tie so it hangs freely away from heat and chain.
At the top, "T" the yellow wire, one leg to the positive on the tail light, the other to the single wire on the headlight. The body of the headlight is self grounding. On the tail light, ground the spare lead, usually black. The black wire on the engine goes to the kill switch. The engine is grounded automatically through the muffler clamped to the frame. Use some black tubing when routing the headlight and kill switch wires from the "T" to the headstock. That makes it a bit more like the original.
Clear as mud?