driving 12 volt load with transistor

I am use to using the 2n2222 for anything 5 volts to 12 volts but it's limit is 800 mA. I am driving a 2 amp load on average (with a 5 amp stall on it)
So I picked up a TIP42 CQ546 but it is not working as expected. When I pull the pin high it pumps out 12 volts but when the pin is low it gives out around 7.5 volts.
What am I doing wrong? Is this the wrong type of transistor or is there a certain way to hook this up?

Circuit please

circuit

New Bitmap Image.bmp (711 KB)

TIP42
http://www.micropik.com/PDF/TIP42C.pdf
is a PNP transistor. 2n2222A is an NPN.
With PNP, high gate = off, low gate = of, just the opposite of NPN.

Will this circuit work if I get the right transistor? Can anyone recommend a transistor to use with 5 amps 12 volts? (preferably at radio shack)

With a 1k base resistor your drive current is 5 mA maximum. If you want a 5A collector current then your transistor needs a gain of 1000 (not a chance). On the basis that it's a logical output (On or OFF), you'd be better using a FET.

how can I use a FET with my large load? can you give me circuits and or a part name?

You can use an N-channel FET just like an NPN transistor. You need to find one with a small enough Rdson at the kind of threshold level where you will be driving it so you don't drop too much voltage and dissipate too much heat.

TBH I would go for a P-channel FET as these tend to have (from what I have seen anyway) a much lower Rdson, but you will need to couple it with an NPN transistor (like your trusty 2N2222) or an N-channel FET to get the switching right:

pfet-drive.png