Hello Brian,
The cables are accessible where they pass through the deck if you remove the trim from around the top of the keel box. There is a thread from last Feb discussing this very topic ("Mast cables"). I found it took a while to remove the trim and I had to be careful.
Unfortunately, at least on Sea Wyche, the cables running above the headlining are embedded in fire-retardant material and so I found them impossible to pull through should they need to be replaced or an additional cable run through with them. There appears to be no conduit there.
As an alternative, I did investigate the run through the headlining from under the port side deck in the heads, above the bulkhead and the heads door to the top of the keel box. I wasn't able to get a piece of wire very far up there before it jammed. Another alternative suggested was to run along the top of the keel box, through the heads and into the forepeak, thence to port and back into the heads to join the existing cable bundle to the switch panel. Very indirect and so less than ideal, of course.
Although the one-piece headlining gives the cabin a good, clean appearance, I have concluded that it is one of only a very few things that I would wish changed in the boat's design. It has caused me a few problems with wiring, mounting internal fittings and limiting options for fitting deck hardware.
Good luck and please let us know how you solve the problem.
P.S. There is a cable conduit inside the mast. Mine had a mousing line running through it, so adding a cable was easy.
Anthony Russell
235/02 Sea Wyche
Anthony Russell
235/02 Sea Wyche