As far as fuse sizing. That depends on how much current you're going to draw, and how big of wire you're using. If your ballsts are 35W each (I'm assuming 2 for 70W total), then 70/12 = 5.8Amps of draw.

The equasion is Total Wattage divided by voltage = Amperage. A 10A fuse will work for you fine, I would also suggest 12ga wire, not because smaller wire can't handle 6 amps of draw, but the smaller wire you use, the more voltage is lost in the wire between your power source and the end point. When your voltage drops, the amps required increase.

Say you only have 10V at the light because you used something like 18ga wire.

70/10 = 7A of draw and so on.

 

07 NNBS Silverado

Thanks for the replies

 

I know on that lower section has RAP power, on the top post, so I'm guessing someone used that as a source for switched power, the other two..your guess is as good as mine. As far as relays, even though it's already been covered, they're immensely useful for many situations. I mainly use them to increase amperage, switch polarity, and isolate circuits, but you can do pretty much anything you can with a switch, and more when using multiple relays.