The "active" headrest is a simple inertia clip setup, nothing powered.
I like this thread. I have a totaled 2005 Magnum R/T donor (bought it new, at 35k miles someone ran a stop sign and T-boned it, totaling it) that I've pulled the 5.7 Hemi out of, along with all computers, and interior. The seats are slated for my '72 Satellite wagon along with the 5.7, but I hadn't even gotten far enough to test-fit anything yet. I haven't done much 'car stuff' for a while at all...but picking up my survivor '70 Charger recently has given me the "bug" again, and I may get some work done on the ol' wagon this winter.
For the wiring, I'd run dedicated circuits to the battery for things like heat, and motors. They draw some current, and I wouldn't want to splice those into existing (old) circuits. Just route two good-gauge wires per seat, directly to the battery. Put inline fuses about 6" from the battery on each wire. If you want, you can even bundle all four together into a separate sub-harness to help it disappear under the hood; run them as a group, to the firewall, then split them off L and R inside the cabin. Ground directly from the connector to the chassis, with a short jumper wire. You can get a large washer-style wiring terminal that can go directly on one of the mounting bolts when you bolt the seats to the floor.
