Howard,
the wiring for the interior lights is run between the moulded headliner and the underside of the deck. If you need to replace the wire itself, you will have a lot of fun pulling the new runs in. When we did our rewire/panel replacement project a few years ago, these were the only factory installed wires we left in place and have had no problems with them so far. We put our new panel over by the quarter berth and installed a new cable up by the old panel to pick up the existing wiring mentioned above. Maybe not the best way to go, but it was the best way without some MAJOR futzing around with fish tapes and hole saws!
You can see an approximation of the wiring positions in the archived E35 MkII manual on this site.
Good luck!