When I did mine, I did run some cables from passenger side to rear to EXACTLY the location you want, for a light switch for my site/day van. But..... I've also fed cables from drivers side to the roof so I do know the route. (Pics below to help). Apologies in advance if some of this you know or have done, it's just 'what I did'.
1. Depending on your requirement you may have to take out drivers seat, you then have access to floor, wiring beneath and bottom of B pillar On drivers side. Pop off the 'B' Pillar trim by drivers door. This will reveal OEM loom going up to roof.
2. Using loom tape, fully wrap your wires for length of rise to get to ceiling. This helps protect and keeps everything neat. Cable tie your new loom to existing loom behind trim.
3. Cable tie one or two lengths of flexi-con to the strengthening rib running across the roof above head rests, and feed cables across to passenger side. See photo 1 with two flexi-cons as I put in a spare to future proof. You can see my additional loom taped to OEM loom so it looks original. In photo 2 you can see the flexi-con over the route. Don't worry though you can affix to the rear of the strengthening rib too, so you don't need to take out the cabin headliner, just the load roof liner which is MUCH easier!!
4. Partially wrap cables to look like OEM loom and you can tape these to the existing loom all the way to tailgate C Pillar. See photo 3. Hard to see, but my cables are sat on top of this.
5. Run a flexi-con down the C Pillar cavity from roof to the middle of the van below the top panels. See photo 4 for route in red. (From recall, you may?? not need to feed a flexi-con down the C pillar cavity but I did as I found it easier to route wires. You may?? be able just to poke them down, but I wanted to ensure they did not rub or chaffe in the blind cavity). For your needs you will need 1 length for the drop down the C Pillar. One length from C pillar to first point of utilisation, 1 length to complete to second point of utilisation. This will allow you to feed cables and get to your terminations. I cable tied flexi-con to the holes along the route as required.
6. Drill two holes on the centre brace in middle of van, insert a small cable grommet to protect wires and feed up tails to where you need them. (sorry don't have a photo of this)
7. As said above, good practice to use edge strip where abrasion may occur as cables pass over obstructions. See photo 5 for example
8. You can see where my switch is sited on photo 6, just to prove thats where I ended up, as you intend.
Caveat to say that as others have posted there is more than one way to do this, but this is how I did it.
HTH?
Cheers.
Edit to say, that once the two flexi-cons are above the front seats and roof liner back, you only have to whip off the B pillar trim to feed wires across the van from driver to passenger if required in the future without faffing around with the seats etc.
so is that some from the C pillar, along the middle and back, and then some along the roof and down the D pillar? If so, is up the B pillar, along the roof to D pillar the better option?
due, in part, to there being windows all round including behind the wardrobe, plus I am rough.
