Can I use my original vintage lighting switch in place of the one included in your kit?

While there may be a way to make this work, it would be best to utilize the switch that came with the kit. First of all, with a new switch you are far less likely to encounter any performance issues within the system, and generally speaking, hooking up a new harness to an older switch is not a great idea. Secondly, our system is engineered around that included switch and incorporates two battery fed inputs. The first, an un-fused headlight feed, is wired directly through the internal thermal circuit breaker inside of the switch, and that is all that is on that circuit. A secondary fused input feed supplies the tail, parking, and dash lamps. This split allows for more of an amperage load directly to the headlamp circuit so that if you are using halogen lamps or alike, you will have less of a chance with that circuit tripping due to the increased load that those lamps can put on a system.