I did this once to have a good sounding powerful radio in the garage that I didn't care too much about. It used to be easier than it is now. The inputs were marked well and you just hooked up things. Now everything has a single plug or two and the connections aren't marked. If you can find the pinout for power speakers input etc. then it will be easy. If you can't find the pin out then you'll have to open up the radio and decipher the connections yourself. The ground may be the case or it may not be. The positive should go directly to a regulator chip. If you can find a regulator chip you can work back from there. It will have a heat sink on it. So will the power transistors so don't get them confused. Get a datasheet off the internet on the regulator used and you can figure out which pin is v+ etc. Find the power transistors and work from there to find the outputs. These will be harder than the power lines. If you cross the signals by getting one line of the right and using it with the left you will probably destroy the output instantly when power is applied. You'll have to figure out where a useable input is if you want to connect the radio to a cd player or ipod or such. If you're lucky you'll find an input jack. Power it from a regulated and filtered 12v. supply. If you're going to turn it up loud and if it has a big amp then you'll need a bigger supply. Good luck.