Nav light won't work, but there's power and new bulb

[vegassail]

I'm perplexed... trying to get the stern navigation light to work.

Using a multi meter, there is 12V at the contacts that the bulb fits in to.

Brand new bulb.

But there's no light.

Tested the continuity in the bulb and it's good.

What else can it be?

 

[Scotty C-M]

Is the bulb making proper contact to the end of the socket it sits into?

 

[vegassail]

I sure think so.

I checked the voltage after the bulb was in, touching the same spots with the probes and got 0V.

No bulb, 12V.
Bulb, 0V and no light.

 

[Don S/V ILLusion]

Sounds like an intermittent connection which breaks down with the pressure from the bulb.

 

[kloudie1]

Probably a very corroded wire or connection.. can pass enough current to make the meter work but not enough for anything else.. When the bulb is in place, the current draw across the bad spot pulls the voltage down.. Look where the wire goes into the light housing and where the wire passes through the deck.

 

[BudGates]

Also try bench testing the light with a battery and a jumper wire.

 

[centerline]

is it an LED bulb?... unlike a regular incandescent bulb, LED's are sensitive to which way the voltage runs thru them...

 

[Tally Ho]

I would take the fixture apart and see what the wires look like inside. My stern light would go off, and if I squeezed the fixture, the light would come on. Turns out one of the wires was badly corroded at the terminal. A quick fix and now have a working stern light.

Greg

 

[pipedream]

It's always corrosion. Usually you have current to the plug, but no ground, hence shows current, but no return to ground to give light, Start at the ground and check all connections.

 

[Doc_holiday]

I too would bench test the bulb, but I would do that with full confidence it will be ok because you ohmed it and your voltage goes to 0. Voltage will pass through the corrosion when there is no load as long as there is a path, but once the bulb is in place the current is too much and this the voltage drop.

Could be at the lamp, the switch or anywhere in between. Could also be the ground bar unless all other power systems on the boat work. I would check for good connection at the panel first.

If you want. Find a 12v light you know works and hook a long wire to one side and the other end of the wire to the battery - NEG. get a jumper wire with alligator clips and connect it to the other side of the lamp. Then you can attach it at various points along the way on the switched wire and see where it does and doesn't work. If it works everywhere, your ground is no good.