I had to do this on my 96 850, and no, I did not have to have it running, just on accessories on ignition.
To unlock a 1995 Volvo 850 radio displaying "OFF," try turning the ignition on and then pressing the power button on the radio. If it remains off, hold down the "Seek" and "Tune" buttons simultaneously for about 10 seconds to reset it. If that doesn't work, you may need the radio's security code, which can typically be obtained from the owner's manual or a Volvo dealer. Once you have the code, enter it using the radio buttons to unlock and reactivate the unit.
Your car has a special 4 digit code It is able to be reset at a Volvo dealer. They will reflash the radio code and give you a copy. Mine was that way and now I don't have problem. For steps in putting the code in look in your owners manual
3223 is the code for a sc-810
You have to take it to a Volvo dealer. They can look up the code in their database. Each radio has a unique code based on the serial number of the radio.
If you have a Volvo roiginal radio, it is likely to be produced by Alpine. Depending on your radio, different Alpine changers may fit.
Look at http://www.volvoclub.org.uk/tech/service/850/WiperWasherSystem.pdf It says it all for a 850!
There's no Volvo 850 2000. What you likely saw was a S70.
Go to www.the12volt.com free wiring diagrams.
need to get the security code from a licensed Volvo repair. code is by VIN.
To reset the service light on a 1997 Volvo 850, turn the ignition to the "ON" position without starting the engine. Press and hold the trip odometer reset button on the dashboard while turning the ignition off and then back to "ON." Continue holding the reset button until the service light goes off, then release it. Finally, turn off the ignition again to complete the reset process.
Fix the problem and the light will go out. Normally on Volvo 850's the ABS sensor goes out (actually a wire comes loose inside the unit) this sensor is under the hood on the ABS unit.