Stumped by Navigation Light on Boat

[BZep10]

The navigation light on my CC rusted out. It was working out to two weeks ago. Bought a new light, before I completed the installation I hooked the wires from the boat to the new light nothing. I put the wires from new light across the plus and negative posts on battery- unit lit up. Next I used a meter to test the wires coming from the boat- I got 12 volts. The light should work, but when I hook the light to the boat wires the light will not light up. I am totally stumped. Any answers?

 

[Baylinerchuck]

Is your new light LED? LED's are polarity specific, where as incandescent bulbs are not. Try reversing the wires. Secondly it could be a current issue where there is enough current to measure on a DMM, (low current draw), but not enough to actually light the bulb. Check wiring connections, especially at the switch. Also check for a loose or corroded fuse.

 

[GA_Boater]

If the new light isn't LED, even if it is, you need a good ground to the other wire. Do an ohms check on the ground wire since the other wire has 12VDC.

Got 12V and ground, then do the reverse check Chuck mentioned.

 

[BZep10]

I was showing 13+ volts at the battery and also where the wires come out on the bow. The light is a two wire system no ground wire. The switch located at the console works- if I shut it off no voltage at the bow wire-turn it on I get the 13 volts on the meter. The light is the same type as the one that rusted-not a LED. The old worked fine since boat was made (2004) except for bulbs and cracked lens. I appreciate your insight. Thanks guys

 

[GA_Boater]

12 volts on both wires?

 

[bruceb58]

The problem is you have a highly resistive connection somewhere. Once you put a load on the wires, the voltage will drop to zero.

Connect your new light back up to the two wires. Go back to your switch and measure the voltage between the switch and ground at the console. If that looks good, leave one of your meter leads on the ground at the console and measure the voltage up at the light. If that measures 12V, the problem is in the ground side. If it measures bad, the problem is in the positive side between the switch and the light.

You will need a long test lead to do these tests. I have a few test leads with alligator clips on each end that I have made up to do these types of tests.

 

[ajgraz]

I don't think you have mentioned how you are making your connections between the existing bow light wiring and the new light?

 

[ajgraz]

^^^Too late for EDIT...want to add to my post above: as some have said, there is likely corrosion, particularly likely at the end of the wiring that connected to your old, corroded (as you say) bow light fixture. So if you're just twist-wrapping some bare wire from the pigtail from your new bow light fixture to the existing--and likely old, black, surface-corroded--"bare" bow light wiring, chances are you're just not making a good connection.