Ah, Yes, those "trusty" vacuum wipers! I used to hate those things. Still do. Your light switch may be OK, because generally, the higher the voltage, the lower the amperage requirement. BUT, I believe the fuel gauge will need help. If the horn has a relay, you could likely switch it for a 12v. relay. For years after most manufacturers went to 12v. systems, there was a wealth of information concerning this type of conversion, probably still is, but it may take a little digging. Try Google and see what you can find. Good luck.