I Have two Hella 500 lamps up on my
roof mounted to my Yakima Load Warrior roof rack.
Finding a way to conceal the wiring
took a while to plan, but I like the way I did it, and it has worked out
great for the past few years or so.
Please ignore the mold and pine needles
in the pics, as it is winter, and I don't wash the rig, and it is pretty
groady right now 
In this first picture you can see the wiring
coming off of the lamps and into some black plastic conduit tubing you
can get at most any auto parts store.
From there the wiring works it's way down
the rubber gasket of the roof.
Yes, it's gross in there.
Parking under a fir tree does wonders
for that.
In this picture here you can see the wires
exiting the gasket and going into the fender between the hood cowling and
fender seam.
It enters into the engine bay and goes
through a hole and into the bay, and from there to the relays.
Here are my three sets of relays.
They are for the roof lights, bumper lights,
and the big honkin' lights I have out back underneath the rear bumper.
Here is an overall MPG explaining how the
wiring is routed.
Click here
to view it.
It might work better if you right click
and save, then view it.
I also have more info on YotaTech in the tech section and in the electrical area on how to wire lights up to relays and the factory Toyota switch you can buy at a dealer.