Hi all, I am refurbishing a Chamberlain "Power Lift" from 1997. I can't figure out where the safety sensor terminals are, seeing that it has four screws on the back, two being used for the wall push button. When I tried the two remaining terminals for the sensor eyes, nothing happened. After putting the sensor eyes over the push button terminals, both green LED's on the sensors lit up but the operator did not respond the way it should have. Yes, this operator does require safety sensors as it was built after 1993 and will not operate the full length of the rail with out reversing. Any thoughts?