Car stereo install in VW Vanagon '91

lol just to warn you this is NOT going to be an easy installation, especially if the vehicle didn't come with a stereo when it was new.

In addition to the direct battery power line and the ground wire, the amp needs a switched 12volt signal hooked up to its remote turn on terminal.  In the harness for your new sony receiver, it will be the blue wire with a white stripe.  As long as that is properly hooked up, the amp will turn on and off whenever the sony is turned on and off.

The amplifier needs a direct connection to the battery, with an inline fuse mounted within 20" of the positive battery terminal.  For that amp you'll probably want to use 8-gauge power and ground wire, and a 40-amp AGU type fuse will work fine for the inline fuseholder.  You should probably just grab an 8-gauge amplifier installation kit because it will include everything you need to hook up the amp to power and to the radio.

The only thing it might not include, however, is extra ground wire.  You might need this if the auxilliary battery is isolated from the vehicle's chassis because if that were the case you'd have to run it to the negative terminal of the battery.  While I'm thinking about it, where in the vehicle is this auxilliary battery? Because ideally you're going to want it as close to wherever you mount your amplifier, as possible.

The RCA cables will hook up to your radio's subwoofer rca preouts; also, you should run the RCA cable down the side of the vehicle opposite the power cable, to minimize noise/interference.  The remote turn on wire can go down either side without any problems.

The reason the amp has preamp outputs is so that you can hook up additional amplifiers without using a separate equalizer or crossover. 

If you have 2 plugs still intact in your vehicle behind the radio opening, that look like they'd plug into this, you'll want to make sure you use one of these harnesses because it will make the wiring for the radio about 10 times easier.  You're probably going to have to run new speaker wiring directly from the radio to the speaker locations though.

If you do not have the plugs still intact you'll have to verify the wire functions the hard way--with a multimeter.

If you need the step-by-step info you should check out Crutchfield's info center.  It's a great starting point and will give you a good idea of what you need to do.