All the information I have shows that there is a radio which sends an output to an amplifier, which sends an output to the speakers.
I want to put in another radio. Should I go through the amp? How would I do that?
Where is the amp?
Or should I delete the Amp from the circuit and run the speaker wires straight from the radio? This seems to be the more conventional method to me.

I removed the amp and the wire harness between the radio and the amp. I took the removed wire harness, cut off 2 of the connectors and wired them to the new radio's harness/ connector. This made for a nice neet professional installation without having to cut up the harness that is attached to the car. A multimter is very helpfull with tracking wires back to the speakers and determining several different 12 volt sources. Dan

1. You need to be sure how many speakers you are operating, and on how many channels before doing the replacement install. For example, some volvo radios run the two dash speakers from the head unit and four channels from the amplifier--the CR-814, for example. Some run 6 channels from the head unit, with no external amplifier--the CR-915 is one of these. Many of the older volvo radios ran 2 channels from the head, with an amplifier plug for two or four channels.
2. Get the wiring diagrams for your car, and verify that they match what you actually have, when planning replacements. Your typical medium-priced glitzomatic radio runs four channels without an external amp. It would not be good to try to run speaker-level output from the new radio into the pre-amp level input of the volvo amp.
3. If you are going to install a non-volvo radio, it would be a good idea to get a volvo harness adapter for your wiring --this plugs into the car and has nicely-labelled wires to mate up with your new radio; it avoids cutting and splicing on your vehicle harness and making changes which might be inconvenient to reverse. Check the search function on the board under ...Scosche... or ...Metra... for a plethora of posts on the subject.
4. plan to spend some time using the search function here, and in looking at the FAQs. All of your questions, including the ones you need to ask but haven't yet, have been previously addressed at great length.

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We have met the enemy and they is us. [Pogo] S70 T5 cop car : Rough Rider suspension, Walmart fog lights, eBay speakers, ambiance by Pall Mall, trim by Le Duc d'Tape, 8-channel THD by OEM amps

Try Crutchfield.com. I got radios for both of my volvos there. They have everything that you need for a perfect fitting radio/cd player, at a reasonable price.

ditto on Crutchfield!! I purchased my Sony head unit from them. They included everything needed to do the conversion, including a harness & detailed instructions on how to bypass the factory amp.

The amp (as fitted OE) should be down behind the centre console behind the lower cubby hole. You can bypass it if you get a radio with an integral amp, by either splicing the speaker wiring or getting a ready made adaptor harness - a number of places do them, here's one which might do it:

http://www.autotoys.com/x/catalog/VOLVO_CAR_STEREO_WIRE_HARNESS_19851992_p_1400.html

If you do a search you'll find it's been discussed here many times.