Is the switch 5 amp AC or DC? Sometimes the DC rating is less. Personally I'd want a bigger margin, so I'd look for a 7 to 10 amp switch. And, personally, I'd avoid the relay and use a higher-power switch, unless I was rewiring the entire headlight circuit. I know (from personal experience) that the connectors are barely adequate, and too much current is going through the switches as wired stock. But adding extra connectors and parts just adds more things that can go wrong, and will make it harder to trace if/when they do.