Ask Kenyons
There will be one, possibly two, cable ducts inside your mast. One for M/H instruments, light and VHF radio antenna and the second, if fitted, for the steaming light.
The duct was confirmed in a response to your question on a similar topic in June 2008.
The problem is how to locate the duct ends at the masthead and heel.
I Googled Kenyon masts and some of their sections have ducts as part of the aluminium extrusion. Other makers often have small "T" shaped projections inside the mast and use a rigid PVC tube slit along its length and slid over the T.
As Scott T suggests above it would be bad news not to have the cable protected.
Why not ask Kenyon where the ducts are and the best way of accessing them?
From dimensions you could then locate any existing wiring and use that hole or possibly even drill another, being careful to go above any other holes at the masthead.
The new cable is often best threaded with the mast up using either an electricians fish tape or a 6" length of bicycle chain on a long thin, (but strong?) mouse line. If there is a M/H light it may be necessary to pull its cable out, pulling a mouse in at the same time.
Mast down only a fish tape will do it other than removing mast cap and heel fittings - which can be a bear on an old spar.
Either way its going to be a fiddly job.
For info - It is written that, to thread the main halyard into the first steel "J" class mast built by Camper & Nicholsons, they tied the mouse line to the tail of the shipyard cat, put him into the open end and all the shipwrights stood in a line along the mast and hammered on the outside in cascade to urge him forwards! It worked.