I am wiring a step for my RV, It had a automatic open close mechanism that has failed, I tried rewiring it using a dpdt momentary rocker switch I crossed the negative and positive and connected the 12v and negative to the center "posts" and it won't work, I wired the switch as a single switch and it works fine, from what I've learned and read it should reverse the polarity and the motor
it's a on.off.on switch help please

 

Are there any markings near the contacts? Or a diagram of the contacts? The common terminals may not be the center terminals...

 

I experienced something similar my self. Check the contacts with a continuity checker or ohmmeter. Some of them have contacts that don't close the way you would expect. I have no idea why they make them with such a strange configuration. If you have one of the "strange" ones, you can't use it for reversing the motor.