Found, after the mast was down for the winter, that I had put a masthead screw right into the wiring
which evidently shorted two wires and caused the strobing. I took the screw out and tested and the lamp worked fine. The next spring I fixed the hole in the wire and it is working fine now.
Three suggestions for testing:
1. Make a good close fitting light cover of light cardboard or duct tape which can slid over the light.
2. When testing, make a connection and wait just under a minute, slide to cover off and see if the light is on, if not, try the next connections, until the light is found to be on.
3. Then reverse the polarity of the two wires at the mast base, and the light should switch from Nav to Anchor
or the reverse.
4. I never test the strobe feature, but it seems to always work ok (3 seasons). The wiring diagram will show what to do to test that.