Question seeking a wiring diagram for a new-to-me boat comes up pretty regularly. I have to wonder why? What drives the query? And yes even if one existed, chances are it's useless. The stuff that doesn't change is pretty straightfoward - there's a switch/breaker, and a wire to the device. For the stuff that changes - electronics - no wiring exists then or now. You have to look for the sub-panel that was wired in, hope there are fuses, and go from there. As a matter of fact, best advice would be to find all the red wires on all add-on electrical/electronic devices and locate the fuse and make sure you have a replacement - could be dozens of them. Good idea to map these too. Will take a while but could really lower blood pressure down the road when something doesn't light-up when you want to leave an anchorage....
The other 'change' stuff is heavy DC cabling because battery installs often change over time, especially with addition of an inverter which can (and likely does) mean the original DC cabling to the panel is under-sized. It can be a bit challenging to locate and identify all the heavy cables and shunts but will make your life easier if you do it upfront with a diagram. Finally, check for over-current protection on the heavy POS cables - often doesn't exist on older boats.
Peter