Hi 500. Your right, an intermittent to a hard failure is a step in the right direction. I have an 04 and if the lighting system is about the same your going to have to pop apart a lot of lights and panels. On my schematics the Dome 10A circuit branchs out like an octopus to feed 12V to ALL the lamp sockets, vanity lights etc, etc. Look at your diagrams to see if they keep the same setup. This line does not even go through the main switch. This line is obviously shorted to ground either at a lamp assembly or this network of wiring. Intermittent at first until vibration moved or wore away insulation to create the hard failure. You could use a meter on Ohms scale but a simple 12V lamp wired in place of the Dome fuse should light to give an indication that the line is at a hard ground shorted condition. When the short is removed the lamp should go off. Or get a BIG pack of fuses to keep popping through for testing. Remove and disconnect all the interior lamp units one at a time attached to this line. If the fault goes away with one bingo, thats the one or the wiring in its immediate vicinity. If you get all the lamp assemblys that are easily disconnected out and its still shorted then its in a remaining lamp assembly or a wiring harness problem. Then you will have to find the numerous junction connectors to disconnect to break this distribution circuit apart until the short goes away. Might be in a door, front or rear body of the van, left or right side, etc. A process of elimination. Good luck!