The tack should have 12v power (with the key in the on position, van off) and a good ground to it and then the wire with the pickup sensor on the blower shaft sending the rpms. I would verify good power and ground with a meter. Does the light in the tach come on?
Apologize for leaving you hanging but I have finally come around to getting this issue taken care of. To answer you question, yes the light in the tack does come on. I adjusted the sensor and even added a washer to move it closer to the wheel. It didnt work. https://shop.truckmountforums.com sent me a new sensor(warranty) and I installed it today and that didn't work either. I have a meter but not sure how to use it in this application. Thanks!