The 3/8" stud is constant power. I'd suggest using a fuse if you use that terminal.

 

Is the radio a regular one and not some speciall high powered one?

You can use the stock red wire being used for the stock radio for the regular operation, which is already fused.

For the constant source which normally is just to hold memories ( stations, audio presets ) you can get the power from fuse block which already gets some sources for that, or even from ammeter ( black side ). No need to get power from outside the cab.

If you don't get a free source on back of fuse box at this moment, you just need to get a female/male terminal On the new radio wire to be inserted onto the batt buss bar provision and splitt the power from there.

Like these

https://terminalscheap.com/piggyback-disconnects

Or use some splitt terminal like some of these

https://terminalscheap.com/double-male-single-female

Your fuse box could already have some stock wiring with those "piggiback" terminals disposed without actual use so a regular terminal will make the job



You can make the same for the Radio main source running to an ACC source of the fuse box, but having the stock radio one so close I think is cleaner. Dunno if you are replacing the stock one or installing down the dash and keeping the stock one in place and operative too.

Modern radios even more powerful than the stock ones are more efficient with the load required. They don't suck more than the stock one. ( actually they use to use less load )

 

I'm using a vintage style aftermarket stereo w modern internals, Bluetooth, USB etc... I used round fuse adapters at the fuse block and connected switched power to the radio fuse and constant power for memory to the cigarette lighter fuse. The adapters slide over fuse end and then snap back in fuse slot. No cutting and very easy.

 

No pics, but here is the fuse adapter I used.