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all the pcm does is close the ground lead to trigger the GPR so if ya want complete manual control just run the ground lead through a 3 pole rocker switch. then you have manual, auto, and OFF.
i wonder why you couldnt find a 9.00 thermostat, set it at 40*, and put it in line with the GPR, but you right, it does sound plausible, and it doesnt seem like the guy is trying to rape you.
that guy has been selling those relays for a long time. they are the same as the $20 relays. i guess it's the 2 year warranty that does it, even with the addition of a $5 push button switch for manual control.
Do your self a favor, and spend that kind of money on a stancor and add the led so you know what's going on. then if you see it's not clicking on (by led) spend another $5 and add the momentary switch.