Speaking of documentation, here is the layout for the relay board. I know you won’t be able to see much at this size but it gives an idea of what documentation I am talking about.
Using this image I can wire up the Vero board that contains all the relays with ease and speed and that is important as it reduces cost to the customer.
Green blocks are fuses to protect the batteries, blue blocks are high wattage resistors to control the charge current when the amp is switched to mains. Light pink are the relays for the left PA, dark pink the right PA, light grey the left Pre Amp and dark the right Pre Amp.
All connections are shown and even the direction they should take so wiring up this board should be pretty straightforward even without using copper track on the board.