Aha...why didnt i just google it !
I remember, what started John tinkering and mixing pickups was when he purchased a mid-80s Carvin AE-185 that he played on the Live video at Carnegie Hall. It’s a semi-hollowbody with two humbuckers and a piezo in an acoustic-style bridge. He thought that was the coolest thing - whether it was one stereo cord out, or maybe he’d just have another output and another cord and plug into the amp, and then switch back and forth, or blend the two pickups. And then he started doing that kind of modification to all his guitars.”
Good read, this
https://www.musicradar.com/news/on-jj-cale-he-would-buy-a-dollar100-guitar-then-if-he-messed-it-up-by-drilling-holes-it-was-okay-that-was-the-cost-of-educating-himself