The rules for DOT and TC state that the placement of the center ID lights (the three in the middle) are to be no further apart than 12" US, and the two outside lights are placed as far out as practicable.

So, find your center one, measure out 6" each way (that's your 3 centers) and then as far to the edges for the remaining two as is practical (I don't know why they use the word practicable).

Of course, your truck doesn't NEED these lights at all (under 80" and under 10,000 lbs), but people stick them on all the time. It's not against the rules or laws to run them unless you ARE OVER 80" wide AND over 10,001 lbs.

Now, the more important thing when installing these is to understand that Dodge trucks have a dual-skin roof system. You will have difficulty running wires to these lights. I was lucky on my PW as I had an original sunroof which I removed that allowed access to that gap between the inner and outer skins. I found a cheesy way to then run the power wire down the A pillar. In hindsight, I should have run the wire across the ceiling to the rear of the cab, then down to the floor, then back to the front of the cab to teh dash.

Too much info?