Ok so wiring up the MSD box is very easy.
First you need to find a place to mount it.
Yeah I know everything is dirty and the box looks like ass, but for 60$ I don't really care cause I got a rev limiter .
I picked here mainly because It didn't get in the way and you can see it in all of it awesomeness, not really. The box is near where I had mounted my coil so I didn't have to find a new spot for the coil, but where you mount it is your choice, just try and make it away from to much heat. I also recommend doing a slight wire tuck like I did. It's stupid easy and you don't have to cut any wires.
Now if you are using it on a 6 cylinder you cut the red wire like I did, but if you are using it on a 4 cylinder cut both of the wires.
Now that is done you will have to cut the stock wiring for the coil, I am pretty sure all s12's are the same but just in case this is what is was on my SE, The red wire (msd box +) to black with white stripe (Stock coil wire +) then white wire (msd box -) to the blue wire (Stock coil wire -) and you can solder them and heat shrink them, or you can crimp them if you have nothing else like me lol.
Once that is done you can now hook up your coil to the msd box, so it's the orange(+) and black(-) wires coming from the box. you can use a stock coil but I recommend just getting a blaster SS or 2 or for that matter any good after market coil.
Now you are almost done. There are 2 heavy wires coming off the msd box, Red (+) and black (-) For the red I ran it straight to the battery with a 50amp fuse in-line just case, and the ground with where the old air box use to sit. I'm sure a good block ground would be better, but where it is now it seems fine. Now you can fire it up, and if you have the 6AL or higher most of them have a built in Rev limter (Soft touch) and you will have a chip on the side of the box. They will have numbers on them saying where it will kick in at, mine came with a 6000 chip so that what I am using. the chips are cheap so you can get a bunch of different type.
Whoops almost forgot, if you want the stock tach to work with out rewiring anything you are going to have to get a tach adapter. If you have a Sun pro, auto meeter tach you can run a wire from the tach straight to the msd box. On the side of the box there is a place to a to plug a wire in, and thats where you do it.
I found these to be a perfect fit
We do NOT use the magnetic pick up line so stay far far away from that. here is the stock how to as well