repugnante

Well you know they have timers/sensors too right? They'll shut on and off depending on the temp. it maybe too warm in the cabin to the point where it shuts off. I know on warm days, if I turn mine on, I won't even feel it. On a very cold day, especially at first intial start up, when I turn mine on, I feel it instantly. The other night the lady and I went out to dinner. It was a chilly night. Afterwards we get to the car and I start it up and turned on her seats. After about a minute she goes, "oooh my butt is getting warm!" That was my confirmation that it's still working pretty well....

mveale

iTrader: (5)

If it was a second-hand dealer added thing, they would've likely tried to keep the cost down as much as possible. Splicing into an existing wire is cheaper than buying a factory trim piece with buttons in it.

Even if it was the car's owner taking it to a shop, they would have to be very meticulous to find the part in question and have the shop wire it in properly. My guess it the conversation went more like this:

Car's Owner: "My butt is cold. Please remedy that as cheaply as possible."
Shop Employee: "Okay."


Anyway, OP, the good news is, you've found why the seat gets warm and the wiring that leads to it. Since you can't get it to work reliably, I would start by wiring them to actual toggle switches instead of the rear defrost. Bonus points for using factory toggle switches.

Hopefully the heaters are wired to a relay and the defrost wire is simply the signal wire. If they didn't use a relay and the defrost wiring powers the seat heaters, it could trying to pull too much current through the factory wiring.

Let us know what you find out!