Audio Systems: aftermarket stereo, cd mp3 player, toyota tercel

Question
mornin' I have a 91' toyota tercel that we installed two head units into yesterday. we installed a soundstorm smp3-100r cd/mp3 player and a jvc ks-f190 cassette player.the problem is that everything works in the car except the two units. they don't even power up when the car is turned on or after we hit the power button on said units. we double checked our wiring and everything seems good. my friend said it could be the fuses is he right, and if so how do i check/change them thanks for any help u can give me on these matters

Answer
Are you using both sets of speaker outputs of these two decks? How did you isolate them? If they are both wired to the same speakers, you may have blown both decks already. If you are using the RCA outputs only then that's not a problem.
You need a test light or digital multimeter to test your power wires and fuses. There is usually two fuse blocks, one in the cab, and one under the hood.