'90 model Camry has the following:
Single DIN-chassis AM/FM radio (some with, some without cassette players)
3.5" speakers in odd little enclosures (with factory passive radiator!) in the dash. Cloth grills will be found immediately under the A/C vents on either end of the dashboard.
Don't try prying these grills off attempting to access the speakers - it won't help you and you're more likely than not to break the retainer tabs that hold those grills on.
It's kindof a complicated process getting at those speakers. Well, not complicated, but rather sortof involved. There's several screws and bolts that have to be removed to get those enclosures out then the speaker is removed from those to be replaced. I have a set of
Crutchfield MasterSheets for the second-generation Camrys. I'll see can I dig it out and post a step-by-step for upgrading the factory speakers.
In the back dash (if equipped with rear speakers) is a pair of 5.25" speakers housed in pods underneath those rectangular covers that can be seen atop the deck surace. To remove these you have to carefully pry up an edge of that cover and get the pressure clips to let go. Unfortunately replacing the back speakers isn't a simple plug-n-play type of affair. They have squarish brackets that bolt into the pod they are housed in and no aftermarket speaker will match the opening. There are aftermarket adapters available if you wish to keep the OEM speaker size back there.
Like I said - I'll try and dig out that set of MasterSheets and post a step-by-step for you.
To answer your actual question - yes, you can benefit from upgrading from OEM stuff.
You won't
need an amp (as in absolutely 'have to have') but depending on what kinda speakers you upgrade to your speakers may never realize their full potential without one.
Unless you get very involved with upgrading your tunes (and it becomes an addiction as all of us here can attest to) you shouldn't need an electrical system upgrade. But after the *bug* bites and you're well and truly sucked in you may in the future....//content.invisioncic.com/y282845/emoticons/naughty.gif.94359f346c0f1259df8038d60b41863e.gif
Have a look at the various stickied tutorials easily found in the forum index. Heaps of helpful tricks, tips, and general info to be found there.
Hope this helps somewhat and I'll be hunting those MasterSheets for ya. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif