Attaching run/on accessory

I would suggest taking this to a dealer. As a service advisor at a Dodge dealership, I have seen many electrical problems caused by customers attaching aftermarket accessories to the TIPM (totally integrated power module or fuse box). This is not to say that you aren't skilled enough to do it yourself -- simply stating that these vehicles have become so complex that simply adding a wire and going can cause other unforeseen problems with the integrated systems on your truck which may lead to problems down the road.