Welcome to the forum, it all depends on how much you are replacing on the wiring. When I decided to change my 50 I rewire it. Since I spent Most of my career working on electric fork lifts which included rewiring I made my own harness. I used a mid 60's alternator with a external regulator, it looks more like it belongs on mine. You'll have to replace headlight and tail light bulbs along with the dash bulbs. You'll need a voltage reducer for the heater and the gauges. You also need to reverse the direction of the wire through the loop on the amp meter so it will show it is charging while running. I replaced the starter solenoid with a isolated type, the positive is on the key switch and negative on the starter button, this way mine will not turn over without the switch on. There is a lot more that I'm sure other members will add.