Wiring a stereo into a 72 Volvo 142

I'm replacing the double din stereo from the previous owner and he had the battery and accessory both wired off the 5th terminal on the fuse Box, but I want to wire it correctly. Is they are an accessory port or a constant on in the fuse Box?

Tldr: where do I connect the battery and accessory power connectors?

It would help to know what components and amplifier wattage ratings.

500 watt JL amp powering a sub with capacitor
2 pioneer speakers powered off the head
JVC kwv320bt head unit

The main problem I had with the old system was every time I started the car up it acted like it was the 1st time it had been booted up because it wasn't connected to accessory power that was always on.

There are several fuses that have constant power, but I would only use them for the radio memory. Use a test light to find 1.

For the subwoffer amp and head unit, I suggest you run a new power supply wire connected to the starter motor B+ pole. According to Crutchfields website calculating max output of 700 watts, you should use at least 8 ga and for longer runs 6 ga - 4 ga wire. Make sure you properly insulate this wire as it goes through the firewall.

I like to use one of these to bring power inside. No rubber grommet to fail and IIRC only a 3/8" hole is needed.