On my JVC
Red wire is connected to switched 12v from ignition switch (via 3 way spliter bullet connection, where wipers get power(orange/white tracer to wipers)
This 3 way splitter is located behind gage cluster. This is where the original radio was connected.
Black wire (ground) should be wired to the ground point on white support bracket behind 3 way splitter in picture above
Orange/white tracer (illumination) should be wired to dimmer switch wiring. I found two blue w/ red tracer wire running from headlight/dimmer switch which powers dash back lighting and heater control backlighting.
Yellow wire should be connected to constant 12v battery voltage to keep radio clock ticking and channel memory saved. Instead of hacking up in-dash wiring, use your bolted connection under the hood on your solenoid (the side connected to battery + termnal not starter.
Schematic:
http://www.fordification.com/tech/wirin ... 0-F350.jpg
As for actual radio installation use the Metra 99-9222 Volvo installation kit (on Amazon or ebay about 20 bucks) for 1974-1994 Volvo's. One of the plates in the kit will fit but to fit JVC's installation sleeve need to cut out with a dremel. Attach it to ears inside dash.
The bench seat in my pickup is from a 69 an has speakers built into rear of back rest. I had my interior completely removed so I ran wires under the floor mat and up behind the seat. I had also bought a set of speakers to replace the old set.
Picture of old speakers
Make a plan, test the radio out of the dash first, use wire loom and zipties to keep things in order in the dash and engine compartment. Pull test all connections when they are made. I used about fifteen 14-16 gauge butt connectors and a few bullet and round screw on type connectors. 16 gauge wire, speaker wire, Wire spripper/crimpers, screwdrivers, beer and a weekend of free time were used to finish the project.
Project finished 
