Most of the car's electrical components get their main feed from an unswitched source, and use a low current switched source to tell it to come on, much like today's modern car radios and amps.
If you desire to have the heaters switched, then you might need to use a relay where the contacts use an unswitched source to turn off/on the heater, and the coil energized from a switched source.
Interesting enough though, the power window main feed is switched through a relay to support its key-off operation, where it will still work for up to 45 seconds from power off.
As long as you don't operate the windows at the same time you operate the heaters, that might work out. It uses a 30A fuse. The power wire is light blue. Be careful though, the master switch has a light blue wire going to the front passenger door to remote control that window. You don't want to use that lead.
which brings up a question (that hopefully someone who understands the electrical wiring diagrams better than I do can help with) - how do the child lockout windows work? I know that the lockout button works differently in the US compared to Canadian vehicles. (In the US, the button locks out all passenger window controls, and also the driver's controls of the passenger windows. In Canada, the driver can still control the other 3 passenger windows.) Basically, I'm wondering if the lockout button just kills the signal for the window to lower, or the window's power. If it kills the power, the child window lock could be a potential issue for the person wanting to use the power windows' power for the aftermarket seat heater use.
The window lockout is part of the windows switch assembly. If it does kill power, it does so within the switch. Since the suggestion is to take the 30A power feed going to the switch, there is no problem with the seat heater. However, that 30A feed is switched to come on at Ig-On and READY power modes, with a 45 second delay in turning off when the car is powered off in case you forgot to raise your windows upon leaving.
Yup. I got them working by connecting the hot feed to the window feed by the fuse box. This way they are fused with the windows along with their own individual in-line fuses. They are 2 level (high and lo) 4 piece seat heaters. They warm your back and bottom and they only draw 10 amps apiece (max).
I therefore turned both seats on high and used the power windows... NO PROBLEM!!! Boy, that really makes up for those cold Iowa winters.
Thanks to all for ideas on where to get the hot feed. This is a great source of information.