Like others have said. Check the basics first; connectors, corrosion
, the switch, the antenna, holes (chaffed areas) in the shield of the coax, perhaps a short to the mast at a chafe point.
Removing the switch is a good idea. It is always best when working on faults to remove as much unnecessary equipment
from the equation as is possible. If you make the antenna reach directly to the radio then connect it directly (or move the radio). Once you have the basic system Radio - coax - antenna working then add the other components back in.
I disagree with PommyDave: you can get plenty of cheap VSWR meters that cover about 120Mhz to 220MHz that will give you a good indication of what is happening in your antenna system. Plenty on EBay for less then 40 USD. I have an old twin dial one that I carry on the boat that has helped several people avoid expensive repairs
coax, if it comes to that, be very careful. It's not just the type RG-8, URM-67, RG-58 etc. that you should look at. There is huge variation in the quality of covering material, density of the braid, whether the inner and braid are tinned or not - in short you get what you pay for with coax cables