If you discover that there is no continuity between the antenna connection at the amplifier/switch and the cable connector on the antenna itself, you probably have a problem in the antenna wire coupling on the roof, probably caused by water getting into and corroding the connection. On the roof, pull up the little rubber sleeve where the antenna wire goes into the roof. Clean out the gunk around the wire and pull the wire up. There should be slack in the wire and there is a coupling that may be corroded. You may need a new coupling and you may need to install a new plug on one or both coax wires. Stuff the fixed connection and wire back into the hole and seal with a good sealant.