testing amps and cd players

I would recommend checking what size fuse is on the amplifiers and using that.  Are you just trying to see if they work, or are you actually trying to find out how much power they produce?  If the former, then it might be easier to wire it to your vehicle battery and test it there. 

If you are trying to test actual power output, then you will need some equipment.  First, you would need a known resistance to act as a load.  A subwoofer won't work as it's impedance will change with frequency.  Just take your resistive load and a volt meter and you should be able to get an accurate measurement of power.  Just make sure the supply to your amplifier is hefty enough not to sag on you as that will effect your results.  Good luck!