Nice I actually just did this to my truck today! Instead of mercury I just cannibalized the brass "bullet" switch from inside the stock light and soldered wire to it. Had a rubber strap of sorts in the junk drawer that was used for bolting up something LOL I forget what but it fit perfect and bolted right up to the hole where original fixture was mounted. Works perfect without the need for mercury and was able to use stock plug no problem!

 

before you burn me about the wire there, its liquid electric taped.

 

And the loom is pulled to the side to show the switch.

 

I didn't mess with the stock loom or mercury switch, I just picked up a variable dimmer switch that works off a key fob for $7 on ebay...