Hold a lighter up to the tip of the probe sticking through the radiator to heat it up and make the fans kick on
The through the radiator probes seem to work good to me. I have a 190 degree probe on my van and it kicks on right when it needs to. With 2 fans there should be no problem with it ever overheating. I would go over the wiring carefully. It sounds to me like it isn't hooked up right somewhere.