I had a similar problem with my Surveyor. I finally ran a jumper coaxial cable directly from the antennae to the booster wall plate. When I cut the booster on, I got good signal. The only other connection that I could easily get to was the connector that came through the roof....the rest of the cable was buried in the walls. I checked the roof connection, the center wire had completely corroded away. I cut the cable back to good wire, replaced the connector, and still nothing. I pulled the microwave out of the wall, and checked the inside part of the connection......again, the center wire had also corroded. I again cut the cable back, installed another connector, and all has been good since.
Chap , DW Joy, and Fur Baby Sango
2006 Ford F150 Super Cab 4x4
2008 Surveyor 263