Things I wish I had known . . .
I have been installing the wiring for the heated seats. The wiring diagram earlier in this post is correct for my seats.
1. The harness comes with automotive type insulation.
2. It takes 4 wires for the switches.
3. There is 18 inches of lead that comes from the center of the seat back or cushion.
4. There is a relay needed for hi low settings.
So - there are several ways to position the components that affect the amount of wire needed.
1. The minimum wire run method would be to locate the switch on the side of your plane near the seat, but not where it can be bumped or things can sit on it. This allows you to mount the relay close by and not have to take apart connectors. You can simply run two power wires from the firewall area. It can be tefzel and be fused either in the seat area or in the panel area. If in the seat area, then you can run +12v/GND and use them for both seats.
Minimally, you might only need ~25 ft of wire for a 2-wire power run.
2. Mount the switches in the panel so they are pretty and can be found easily. Then mount the relays close to the switch, a short power run to the switch, then three wires for each seat. This is a 6 - wire option for both seats. My wire run for this configuration (3 wires) was 12 feet from the panel switch to the seat locations on a -7. Yes, that is 3 wires X 12 ft ea X 2 seats = 72 ft AND I had to take apart the connectors, remove the terminals and reassemble.
I mounted the switches in the panel before I knew the diagram because others were done that way. I chose tefzel wire as it was going along with the other wires in a bundle and it just felt right that they were all the same.
So now you know what you are getting into, either way.
Here is a picture of the heating elements, switch, and harness. Sans relay cube.