I found this fantastic little mod on YouTube while looking for another schematic. Temporary (or permanent) wiring harness to see if you want to jump an active instrument to an 18V system. Just made one of these for a friend who isn’t sure if he wants to go 18v but he wants to try it. Having the headroom makes sense if you can swing the space in your control cavity.
I love that you can hand off the harness and let the new owner figure out space issues in the body cavity for the second battery on their own time. Plus, it’s temporary…with the option to be permanent…so you can try it out and reverse it if you sell an instrument. Or keep it installed. Win win for everyone. Love learning little tricks like this.