Ahoy and welcome to CF Parkerrodney59!
-Does anything else on the boat
-Was there a 'mis-wire' or 'mis-power' event on the boat
while the spreader lights were turned on?
AC in of itself reverses polarity 50 or 60 times a second depending on the source. The spreader lights are most likely 12 volts DC unless your boat is wired for 24 volts DC. Depending on the make and model they will either be polarity specific or not.
Like ChrisR mentioned, most likely some sort of chafe (short) or loose connection (open) in the spreader light circuit or the circuit feeding the panel. If there is some sort of connector at the mast
, you might be able to diagnose whether the issue is in the mast or in the other wiring
of the boat.
There are books
by Don Casey and others by Nigel Calder that give good overviews of boat system. Diagnostics take time and practice. I spent part of a weekend removing and testing a starter on a motorcycle when the issue was really the battery
. Sometimes the problem is bold and staring us in the face and we look elsewhere...