Also remember when chasing antenna wires that (assuming they are on an A- frame) there may be a hidden connector lurking somewhere.....
Also might be worth checking the wires in the connectors themselves. CAREFULLY (on grounds you don't sound like you do this all the time!
) unscrew the antenna plug -they are not too dissimilar to a TV aerial or satellite cable connector - it's worth opening the plug(s) and reconnecting with a fresh end of wire.
If you find the copper in wire ends is all black, just replace them (one at a time!) with new wire. Maplin do rolls of single core in a variety of colours. On a similar theme - check your battery cables - if they have black copper at the ends, the intermittant operation might
be down to a lack of voltage to keep the kit alive.
Also as a thought ref. your GPS antenna - is it on a 4 pin connector? If so, google "NMEA2000 for beginners" & check you have the correct end caps & the Ts aren't wired @rse about face. There was a change from one single resistor end to one at each end - you may have a mix?
...and call back here with Qs about what you find - enough of us have been there before
to find an answer...