There are two stranded wires coming to the connector. Definitely looks like a 12V connection for something. Threaded plastic cap on the metal connector body so something that is meant to be installed & removed, not there all the time.
Detroit 6v92TA
(Low profile's)
Alison Gears
Westerbeke
12.5kw Genset
Definetely looks like 12v connector, but as mentioned lights or possibly tv antenna, old analog gps. But try putting a meter on them and turning things on and see what's. Worst case you have to trace them back to the source.