12v constant + 12v switched for radio

[rearwheelpeel]

I’m putting a new head unit in my 76 242. The green book for 1976 wiring diagrams doesn’t show anything for the radio as far as I can see. I want to replace the rats nest of spliced wiring with new wiring directly from the fuse panel. I need a 12v constant and a 12v switched power source. Should I just hook up the multimeter to the fuse panel and go with any old constant power source? Or are there 12v constant + 12v switched fuses someone could suggest I use? Am I overthinking this? I’ve wired radios but never “from scratch” in a car this old and I guess I’m a little intimidated. The old head unit that was in here had the constant and switched lines tied together, so it would reset the radio and presets each time the car was started. I’d like to wire it the correct way.

[Radtap]

I ran a wire from the junction behind the battery with a fusible link for my constant

[philski o'flood]

can you trace back the radio wiring to a 9 pin square connector?

Check the fuse panel cover, the label should show Radio there on some circuit, also should show switched and constant circuits too