I am looking into upgrading my volvo soon. I already know what kind of stereo I want and I know how to mount it, but I want to put an amp in the back along with a few nice speakers. I have a fold down back seat allowing access to the trunk I was planning on putting a big speaker there. Also I want to put in power windows and maybe even an air conditioner.

A few questions: If I put an amp in will I Have to wire it directly to the battery? If not how will I power it?; Are power windows hard/impossible to put in?; is behind the back seat and okay place for a large speaker?; Is an air conditioner hard to install... actually come to think of it I may just need to repair mine... ex nay on the air conditioner...

As far as the amplifier is concerned yes you do have to run a direct line from the battery to the amp .
Good news is there is a firewall plug located under the driver's side dash that you can unplug and run the wire through. However you will have to take the seats out and run the wire the rest of the way under the carpet, this process is not too bad I did it with my own car (83' Volvo 240 DL) and to get the seats out you only have to remove four bolts. The back seat is on a latch and you have to pop the bottom of the seat out first and remove it.

Now as for putting a speaker in behind the back seat. I assume you are referring to a subwoofer and in that case I would recommend placing it on that second shelf of the trunk as to leave room for other things you may want to transport.

Any other questions feel free to ask.

Actually yes. What is a good sized subwoofer? I mean I am not going to be driving down the street making my car bounce, but I want to be able to provide some outside music when I am hanging in empty parking lots with my friends and stuff. My dad is an electrician so running the cables won't be a problem, but is there any easy way to run the cables where they can't be seen? (Or were you just telling me how to do that?)

Yeah i would say run the cable either down the runner and then into the trunk or directly under the carpet. Also make sure when you are running the digital audio cables to your amplifier that you run them separate from the power wire or else you will have noise interference in the line. I would just recommend running the power on one side of the car (driver side) and then the digital on the other side. Then you just run the wires up under the back seat and through the cargo extension.

Now as for what size of subwoofer would be efficient.

I have a 10" Rockford Fosgate T2 subwoofer that can bounce my car pretty good. Depending on what type you get I wouldn't recommend getting any larger than a 12" and I would say only purchase one and not a pair. Why? There just isn't enough area space in the trunk.

Let me know what type of subwoofer you are considering and I'll give you some more input.

You will need to keep the power and ground supply cables as large and as short as practicable, or it will sound bad on higher volumes. If you go into sufficient power useage, you may need to upgrade your alternator, and some main power feeds for the extra load they'll be carrying. Electric windows are just something more to go wrong, and they do, so leave them out. Too much noise will shake even an old 2xx series til it rattles apart, so please be kind to all concerned. If quality sound is required, then sound damping cloth padding will be essential in the car and particularly a wagon, which is voluminous enough to really boom at LF. The long-term fatigue and debilitating effects of such exposures are still largely unexplored or ignored. Capacitors at the amplifier can only do so much to keep the voltage up, and they're not cheap when they get big and hi fi quality. From a technical viewpoint, it's better to put the amp forward in the car, near the battery(/alternator). Compromises have to be carefully weighed against performance downgrades. Nothing is easy. Perhaps the best way ids to step the supply rails up a bit, transmit the power and the regulate it back down to a steady state that won't downgrade with loading-but that's $$$ and Watts (fuel!) down the drain, IMO. But it works.

A few adventurous types have installed power windows from the 240 GL or Turbo into the DL models. I'll try to find the links for you later. I hope to do this myself sometime soon as hand-cranked windows in the 21st century just is not practical.
Since you have a 1984 model, the hood blanket from the 240 Turbo is a direct fit and will lower the dB in the cabin a lot which will help with the sound quality.
With the A/C in the South it is pretty essential , if you're lucky it may just need some new seals and a recharge but your system will have R-12 and getting someone to work with R-12 is getting tough these days plus R-12 is getting really expensive. If you're unlucky the compressor is bad. You can convert your system to R-134 but if you're going to that expense, it would be better to install the 1991-3 system for the 240 which is much better.

I need to go back to best buy and make a thorough check on which sub-woofer I want in particular, but you guys have given some very helpful feed back thank you. I don't think sound quality is on my top list of importance I don't hear a lot of that stuff. I don't know how to explain it, but my Dad has it to and he explained it very well. Like a record and a cd sound the same to us. I mean we can hear the music just not... lol idk. Also like I said I don't really want to boom my car.

I have been thinking though. Would it be easy or only mildly hard to put a speaker under each seat rather than a sub-woofer in the back? That would keep the speaker in the front, provide the music I crave, and still be loud enough to hear outside the car.

If my AC is completely broke (i.e. bad pump or the like) I don't have enough money to replace it, so I'll have to suffer, but if it is something like seals or a recharge I think I know a guy who can fix it for cheap.

Does anyone know where I can find a battery for this tank? I bought a used one at a junk yard, but it was dead. Walmart used to carry them, but I can't find them anymore. I am looking for something not too expensive. I found one for $75, but I was hoping for cheaper.