Good Method to Add Wiring For Add-Ons

I found a female spade terminal on the outside of the firewall, where the wiring harness turns from along the firewall, and goes towards the starter relay.
I’m not using it, and it’s only hot with the key in run position. I’ll check the voltage on it before I use it. (For my add-on fuse block.)
Everything else is working except the dash lights. Good fuse, can’t find any juice and it’s a real pain getting my old self under the dash.
I thought the turn signals didn’t work. Turned out the flasher was verrrry slow to click. It didn’t like getting back into service. lol
Some of the parking light sockets were corroded, but they cleaned up.