The console provides 12V power already so I used that, you'll solder Shane's 12V AND the swtich on the same wire, I had a large ground ring already installed when I put in the stereo amps so I used the ground for it but you could use the 12V ground on the console side too. It's hard to tell but you'll see two wires spliced in on the 12V pigtails on the console in the pictures if you look closely.
I've seen guys do it under the seat too but since the stock heaters are on the same fuse as the rear heater that I don't use anymore I opted for that and put in a smaller fuse, I think I went from the stock 25 to a 20, figuring any issues that I might have would end there rather than a burned down rig. I chose the console tap for power only because the seats always have power, they are fused but are always hot, I wanted to make sure when the key was off everything was dead seat heater wise and I wouldn't have to worry about any transient drain problems later.
I like you was doubtful and worried so I opted to just plug in a switch pushing the wires into the console pigtail first and making sure everything worked on the seat side with a meter. You don't need to power the heaters yet to do this, you're just checking to make sure the high/low signals are being sent, the LED's work, and everything is dead when the key is off, it definitely will install confidence knowing things work before you commit to nipping and soldering . I don't know how much you've soldered but a quick tip, tin both ends of the wire first, this way you can just heat them both up and stick them together without fumbling for more solder.
You'll notice that on the seat sides to the matching console there are TWO wires that are identical because they actually run to and from, these are the HIGH LOW wires that you'll use yellow and blue from Shane's kit, you can either splice them in under the seat or push out the pins on Shane's connector and slide them into the stock like I did. Put them under some good light and you'll see that Shane's connector has a locking tab, undo that and then look inside the back side, you'll see the catch that keeps it in the connector, slide a small screw driver up inside that as far as you can, NO BRUTE FORCE HERE, and then firmly hold the wire and the screw drive and pull back out, should slide out with minimal resistance, if you deform the hump on the pin don't worry it's pretty easy to straighten out, just no BFFI (brute force and effing ignorance)
DON'T forget the diode, I had done the DS first and then forgot to add a diode to the pass side AFTER I had already soldered it all, PITA. I doubled up on shrink tube and then used that cheap snake stuff found at harbor freight to wrap and then 3m black tape.
Since I was worried about the pigs being long enough I put them in the lower slots, you'll have to scrape a bit off the ends of the console to do this or you can't orientate them the right way, this gave me enough room to pull the connectors thru and plug the switches in. Mine was tight because I put 3 additional 12v outlets in the front console and 2 more in the rear and customized what was the rear heater outlet to LED panels that light up the back floor when the rear doors are open, so getting the consoles back in was tricky to say the least because I had a half dozen wires in the front and rear console to contend with.
If I get some more time I'll video the pin removal with the other end of Shane's kit under the seat you'll have the extra black and red wire, there are really only ONE red and ONE black going into the control box, they're just spliced together, you can feel where if you run your fingers from the control box back to the first four pin pig tail. I thought about stripping them back and nipping them but folding them over and shrink wrapping the ends seemed much easier to me plus it leaves the pins on the wires should I ever need them again, of course the red will be hot when the heaters are on so double shrink or tape it, you don't want it coming in contact with the metal on the seat bottoms.
OK rambled enough, hope I didn't confuse you more!
