I assume you are deck stepped, not
keel stepped. If so, see if this will
work after you
Google "waterproof
electrical bulkhead fitting"
Connect the two
cables and seal their connector.
Drop a plum string down the mast to pull the cable up from the bottom.
Pull the cable through the bulkhead fitting and down into the
cabin wherever that hole is. You may need to create one and seal it.
Follow the other mast
wiring above the
cabin headliner or from the base of the
compression post to your display. At some point in the
route, typically in a locker, will be a location that you can loop the extra cable to have it and the box out of sight.
When you loop it, try to attach it to the inside top of the locker, so that items dropped in the locker don't damage it.