boat lights

[Redbone]

What is the difference between the two prong and the three prong navigation lights?  I am in the process of making sure everything is working on my boat and I bought a 2 prong light. It doesn't work in the front, three prong, socket. The back light works and its a two prong.  I tested the light I bought in the back socket and it works OK.  I am pretty sure I have power up front.  I am hoping I just need to buy a three prong light and everything will work OK.  Any info would be a great help.  Thanks!

[Frank]

check the boat part of the connection with a volt meter.

[Redbone]

I have power... Must be the three prong instead of two?