You can join the switched and non switched together and just wire to a fused acc. Live
problem with this is the possibility of leaving one or both switched on with the car engine not running - I think a flat battery would be the result.
The kit I have uses the ignition feed to activate a relay to allow current to flow through the warming pads. Ignition off and no current flows so no flat battery.
just re-read and you did suggest acc live, but on my fuse box that's not the easiest to find as it certainly doesn't follow any of the published diagrams.
cheers
