My St60 wind instruments on my 44 have packed up after a short period of giving spurious readings. I have been told to check the connections below the mast before I invest in a new masthead unit, but where are they situated? There is not an immediately obvious inspection plate to open.
if i remember correctly a wire bundle exits at the bottom of the compression post under the floor boards. lift up the boards around the post and trace from there. your boat model may differ location. good luck.
On my 37 there is a removable panel on the deckhead around the top of the compression post underneath the foot of the mast. Connections in there. Best of luck trying to trace the problem.