Troubleshooting Nav Lights

[jwilcoxon78]

So my navigation lights keep throwing the breaker when I turn them on. I've swapped breakers with the same result so it does not appear to be a weak breaker. I removed both light bulbs and it still threw it. After check resistance from the power side of the switch to the ground terminal joint, I'm only getting .5 ohms so it does not seem that there is any meaningful resistance.

Any ideas apart from rewiring the nav lights?

 

[smokey73]

Probably an insulation break down or exposure/open of the hot wire or even the ground wire. Take a look where the wires make sharp bends or go through fittings. If your nav lights go up through the pulpit look particulary where it goes into and exits the pulpit tubing. If you find such a spot you may be able to splice in a new section wire rather than rewiring. In any event, if it is caused by a wear point you will need to determine and fixe that since it could repeat itself.

 

[Justin_NSA]

You may be the victim of chafing.

 

[jamieFL]

Forgive me if I'm wrong, but a dead short would be 0 ohms.

0.5 ohms is a short none-the-less.

 

[smokey73]

Make sure power off to your DC panel. You do not generally take resistance readings with power supplied

You should have very little resistance ( 0 or near 0) across the closed breaker if it is good (power side to load side of breaker). You should have infinite resistance across the breaker when it is open.
If you've already swapped out to use a known good breaker and it still trips is probably not the breaker.
MAKE SURE DC POWER IF OFF AT THE PANEL
You should have 0 ohm or only a very little between the power side of the breaker and the power side at the light fixture.
If you have infinite ohm then it is an open, which will keep the nav light from working but shouldn't trip a breaker
DO NOT DO THIS WITH DC POWER ON - IF you have 0 or near 0 ohms between the power side of the breaker and ground, you have a short, which should trip the breaker (That is what the breaker is designed to protect the circuit from - ie overcurrent). That is what I suspect is the problem based on your description.

If the breaker is tripping it is an overcurrent situation, assuming the breaker is good. That is what breakers are supposed to do.
You said it tripped even if the bulb was removed. This almost certainly indicates a short or high resistance short to ground (ohms above 0 but not infinite) somewhere in the wire run from the breaker to the fixture. Look for likely places were the wire may be tightly bent or where it goes over something that could chafe it.

 

[rgranger]

Forgive me if I'm wrong, but a dead short would be 0 ohms.

0.5 ohms is a short none-the-less.

Correct!

 

[Regular Guy]

Yes,
it seems to be confusing for some but 0 ohm is the highest resistant you get, a total short,
and the measure infinite ohms represents an open circle, means no resistant for the current at all.

 

[jwilcoxon78]

Thanks All. So I turns out then that I forgot how to read a multimeter and I in fact have a short. On to the search for the break I suppose.

 

[rgranger]

Yes,
it seems to be confusing for some but 0 ohm is the highest resistant you get, a total short,
and the measure infinite ohms represents an open circle.

I don't think that is correct. Zero ohms means no resistance and you have electricity going straight to ground without passing through a circuit. The large current would throw your breaker. So zero ohms represents a short in the system someplace.

 

[smokey73]

Yes,
it seems to be confusing for some but 0 ohm is the highest resistant you get, a total short,
and the measure infinite ohms represents an open circle.

Not stated clearly Regular guy. You are right it is confusing
0 ohms is the "lowest" resistance (ie no resistance to current flow) not the highest resistance.
Highest resistance to current flow is and open and is represented by infinite ohms.

 

[smokey73]

OP seems to "have seen the light bulb go on" so now he can get on with figuring out where the short is located and fix it. Glad we could help get you on the right page with a multimeter. Best of luck with tracking it down.

 

[CrispyCringle]

OP said he checked "both light bulbs". There should also be a stern light (white), and steam and anchor lights on the mast. I would start by opening up the light fixtures and looking for obvious signs, like corrosion, broken bulbs (the bases). If that turns up nothing, then pull the fixtures and check how the wires are attached. Also, if the mast is like my H23.5 it has a cannon plug for the mast lighting at the base and is a pretty crappy design. It may easily have crumbled on the inside. Also, if the mast wiring has a plug as described, try unplugging it and then retest, so you can isolate the main wiring from the mast light wiring.

 

[jwilcoxon78]

OP said he checked "both light bulbs". There should also be a stern light (white), and steam and anchor lights on the mast. I would start by opening up the light fixtures and looking for obvious signs, like corrosion, broken bulbs (the bases). If that turns up nothing, then pull the fixtures and check how the wires are attached. Also, if the mast is like my H23.5 it has a cannon plug for the mast lighting at the base and is a pretty crappy design. It may easily have crumbled on the inside. Also, if the mast wiring has a plug as described, try unplugging it and then retest, so you can isolate the main wiring from the mast light wiring.

Thanks CC. I did try to disconnect the mast plug but got the same result. Once I'm back at the boat, my plan is to (after removing the battery cables) to remove the three power wires from the switch to then individually check them for resistance to the ground wire. Hopefully this will at least get me the to right wire to focus on. Worse case scenario then is to tie a new wire to that one and pull it through from the other end.