Building a heater into rear defroster blower hose

'273:

Both Ford & Cadillac did that electric defrost with the 3 phase connection. I still have CS144 alternators on the shelf with the 3 phase connector on the back. It was an elegant solution, because it kept that load off of the rectifiers.

A 20 amp heater for a rear defogger should be wired straight from the battery with a relay at the heater & a fuse or breaker at the battery. Most OEM systems draw more than that, and are in cars with alternators three times the output of that ancient mopar design. I would plan on upgrading the alternator for a whole lot of reasons, but that is another thread.

Rice:

You seem to be making a lot of assumptions.
None of the 20 buck chinese crap has any sort of thermal protection. They don't care about your car, and warn you to "unplug the unit when not in use" . One of those links is a hair dryer. Do you really think it was designed to run more than 5 minutes at a stretch?

If you really only want to spend 20 bucks on the solution, the next time you are at Harbor Freight:

http://www.harborfreight.com/12-volt-rubberized-heater-with-fan-96144.html

It is the same as one of your links. Go plug it in, and see how hot the cord gets after 5 minutes. That should tell you about the rest of the quality.

B.