Assuming yours is the same as my 1983 with Isomat mast, the wiring is in a plastic channel. Extruded into the inside of the mast is are two T's, and a plastic channel (basically a square tube with a slit in it) is slid over each T. One terminates at the spreader light, one goes all the way to the masthead. The wire is pulled thru these channels but is loose otherwise - not tied together nor tied to anything else. Once the wire is disconnected from the light, straightened to slide smoothly, and pushed back into the mast, the only thing holding it will be a little friction in the channel. It should slide right out.
I wanted to slide the channel down a foot on mine to afford a better angle on a new antennae wire exit at the masthead. Couldn't get the channel to move for anything. I found that the rivets on the winch pad mounts were right next to the T and the rivets had extended into the channel and locked it in place. That could possibly cause some friction/jamming with the wiring too although my wiring ran free. Once I drilled out the rivets the channel slid right out. As an aside, not sure you can find the plastic channel anymore if you find it broken. But I found that Schedule 20 (light weight) PVC pipe (3/4" or 1") readily available at Lowe's works just fine. Just make a jig to push it thru a tablesaw to slit it.
