Noticed your location. Is it ever humid there?
Pull the 14 pin connector at the rear fuse panel and look for corrosion on the pins and sockets. especially on pin #10 Your intermittent voltage could be due to a poor connection.
You should also carefully pop off the cover of the 14 pin connector and check that there is no corrosion in there, and that none of the wires are touching each other. If you accidentally pop all the pins out of the housing I can tell you where they all go.