system setup w/ relay

Hey i have a system that uses a large amount of power, in my last car i had my main battery that ran to a relay, the relay was grounded at one point and the other point went to the ignition or something. Then from the relay it ran to a second battery and then to my amps. I believe i bought the relay in order to have current flowing with the car on, but not while its sitting off with the key in so i can listen to music off the back battery and not pulling from the engine battery. My question is, where do i wire the ignition side of the relay to? Obviously the ignition, but last time i was thinking i could wire it to a switch turning it on and off myself. but that sounds kind of annoying. I drive a 97 toyota 4runner, curious where i wire this ignition side to? I attached a picture its simple really. I just dont know if there is a certain part of the ignition or really how it works at all... I just want current to flow when the engine is running and that is it. Thanks hope to hear back. Chris - 97 Toyota 4Runner

Alpine CDA-9884

Kicker SX1250.1

Kicker 15" L7

Ground the black wire

Connect the ignition to RED / BLACK @ ignitionConnect CURRENT to postive terminal of the batterythe other side (load side) connects to your amps.

thats a battery isolater or a super big relay.

could be a battery isolater? lol i guess i just have to find the RED / black ignition wire. where do i startChris - 97 Toyota 4Runner

Alpine CDA-9884

Kicker SX1250.1

Kicker 15" L7