If you wonder if there was a reason for the routing, EY (at least in the 80's) was trying to follow 'best practices' and avoid routing wiring thru the bilge. I have seen an O'Day and a Catalina from the late 70's with major wire bundles that went thru the damp/wet bilge areas -- expedient, but a bad idea.
My previous 26 footer was not an Ericson, but did have an internal frp liner, and all of the factory wiring was routed thru/over that liner. Since that '81 wiring was all un-tinned, I can only hope that by now a subsequent owner has rewired that boat. (!)
My SWAG is that some of that wiring, which was a minimal systeml when your boat was built out in the early 70's, is really hard to pull thru. Not sure of a solution, since normally one would tie a pull-string to the wiring and pull it thru, and then run new new wiring. Some "imagineering" may be involved. We all take for granted a *lot* more circuitry in modern boats for both 12 volt plus AC panels and devices. Plus... instrument wiring and coax.
One note about that liner: you can create very tidy access places with matching plastic(Formica) covers here 'n' there for getting at hardware and for running wiring. Also by installing 3" pop-out plastic access plate fittings. Sometimes a hole saw set is your friend.
The ease of cleaning and general appearance of the full-liner boats is sometimes matched by these sorts utility access quandaries.
But then, if maintaining a classic yacht was easy, they'd let just
anyone own one!