I'd like to run my radar wiring inside the mast on my 1998 34' Catalina. I've looked for access panels but there aren't any (that I can find). How can this be acheived?
Your C34 is considerably newer than my tall rig 1988 C-27 but I thought I'd relate my experience. This past spring we replaced the masthead wind transducer and replaced / cleaned up all the lights & sheaves.
From the masthead to the base of the mast there is a tube (PVC?) for wires, with a hole cut mid-mast for the deck light. You will probably have to step the mast (take it down) in order to run a new wire using a long "fish".
At the base of the mast, coming from the deck plate, there are usually quick disconnect plugs for the VHF and lighting cables. These are inside the mast when the mast is up, of course, hence you need to step the mast to gain access to them. From the mast step plate down is the compression tube, which leads the wires to the forward part of the bilge. I had to completely remove the mast step plate and use the steel fish to pull the wire through. And then use copious amounts of silicone sealant when I put everything back.
I had the boatyard crew help me step the mast and put it back up, rather than try to do it myself and screw things up. (I'd never done it before.) My boat was drydocked at the time because we had new through-hull transponders installed too. We had bought a Raymarine ST60 kit.
Good luck!