Simple Car Stereo hook-up questions

I have got an in-dash AM/FM stereo that I’d like to install in an MGB. No installation kits and no handy wiring harnesses, just ‘hard-wired’. Trouble is, I don’t know where all these wires are supposed to go! And nothing in the manual. It’s an Aiwa AM/FM/tape meant for four speakers. So beyond the four sets of speaker wires off the back of the unit, I’ve also got a fused red, a fused blue, a plain black, and a plain yellow that goes thru an Aiwa supplied fuse block (at least that’s what I think it is). I’m sure one of these fused lines is for switched power and another is for unswitched power, and the black is for ground, but what’s the other fused line for? Rather than me acting like I know it all why don’t one of you just tell me what they’re all for? Also, what size fuse ought to be installed in the fused lines?

Also, anyone know of a short chassis, single DIN, CD player?

Thanks,
Deadeye

Have fun...

Most MGBs electrical systems are wired for reverse polarity, unless you've had a conversion done. Your yellow wire is constant 12V, or unswitched, red is switched ACC and black is of course ground. The blue wire is for either power antenna or amp turn on (or both). You probably wont need it unless the car has a power antenna, or if you're adding an amp.

Be extra careful when working with the wiring in that car... MGBs have some of the worst reputation for poor wiring from the factory, an amongst other things a lot of the circuits are not fused, so keep that in mind. Good luck.