Derale 16749 question

[Kaptain Kadian]

I am running dual electric fans on my 70 c10 with a derale 16749 thermostat. Today, I went to start my truck for the 1st time in a while, and noticed that 1 of the fans came on immediately when I turned the key to on. It isn't supposed to come on until the coolant has cycled and the truck has warmed up. The next problem was that the other fan never came on. I adjusted the setting in the thermostat to see if I could get it to come on and it never would. They both had been working properly the last time I checked them. I had another sensor that you insert into the fins of the radiator, so I hooked it up to see what happened, and neither came on. This was what I expected since I didn't insert it into the radiator. So, I figured I have a bad temperature probe, but seems weird, because I have had it for about a year and have barely driven it. So, do you think it is just a bad probe? I don't have time to strip the wiring on the 2 fans to hook each up to a battery to test them tonight, but that will be my next step. I don't know the voltage if the fans, but I am wondering if the thermostat is capable of powering both of them. It had ran both fine for a while, so I am not sure. Any other ideas of how to check them? I hope a while just came lose or something with the other fan.