There could be a fuse, then again there may not, it depends on the person who wired the system. A seatch of the
SeaTalk cabling should not take too long. The only other fuse in a
SeaTalk system I am aware of would be in the
autopilot, but as you have a Robertson unit we can exclude that.
You will have to take a methodical approach to trouble-shooting to determin where the
power originally was sourced. Of course, you could also introduce an alternate 12V supply to the SeaTalk system.