Finally a new deck plug for mast lights ...but how to make 2 wire into a 4 prong

[hockeyfool]

Got a decent stainless deck mount plug receptacle for the mast light wiring, but as my mast has
4 wires - and the old plug was worn past ability for threaded stop nuts to hold the wires,
    I bought a 4 prong - so I could insert all 4 wires into the 4 hole female end . One light burns even
brighter now but the masthead light does not at all.  any idea how to utilize this 4 prong plug for all 4 wires ?

[MacGyver]

What all needs connected?
For most 4 wire jobs I make a common ground wire, making all the grounds go to one terminal in the connection, typically utilizing the larger pin..... just my preference.
That would give you 3 connectable connections for power there.

Mac

[brackish]

Mac is right, one of the wires should be a common ground and it should be connected to the larger pin.  Then there should be a separate wire for the masthead anchor, the steaming light and the deck light.  Good to find out what each is and lable them in your mast.  I did that by checking continuity to the ground then jumping directly from a twelve volt source to each wire with the ground on the negative terminal.  Lit them all up then labeled them.  Should all be color coded so you can match them up on each side of the connector. 

If you can't get one to lite up when properly connected, could be a bad bulb or socket in the fixture.  I actually had a ground fault from the original installation that was kicking the breaker, one of the screws that connects it to the mast was making contact with the socket,  had to tape it to isolate.