ok this is the second time this has happened. the first time i got a new one and it worked fine. but it only happens when i tear down the manifolds. sometimes ot'll come back, but usually its just dead. any ideas? ive checked the grounds and power wires and all. is this guage toast? if so whats causing it?

 

Maybe you pinched the O2 sensor wire in the process? Or damage the connector at the sensor?