Navigation light fuse keeps blowing!

[MagicalArmchair]

The motoring nav lights on my pulpit I noted hadn't been working since my deck repaint. I assumed the terminals were corroded on the bulbs, so got to work cleaning them up one evening on our summer cruise. Tried them again after cleaning up, and no luck. I went below and took a look at the fuse, and boom, noted it had blown. I replaced the fuse, and snap, the lights dimmed for a sec, and the fuse blew again. That fuse just juices up the two nav nights on the pulpit, port and starboard. If, from the appliance side of the fuse, I disconnected the green starboard wire, the fuse no longer blew. If I unplugged port, and plugged back in starboard, the fuse would once again blow.

From the pulpit I unplugged the nav light, (fearing the light unit had a problem), replaced the fuse and the fuse STILL blew. Out of time by now, with the 1st mate accusing me of waking up our daughter sleeping in the fore-peak and it was time to come to bed myself, I grumpily gave up my fruitless diagnostics.

The below photo is directly under the pulpit in the anchor locker, the chocolate block attached to the ceiling. The green (starboard!) wire in the below, goes all the way back aft to the bottom of the fuse that keeps blowing. I can see in the below, the green wire looks corroded where it enters the hateful chocolate block. Do we think this could be the problem? My eletrickery skills are somewhat limited!

My next step is to replace the chocolate block and inspect\cleanup the wires here. Any other suggestions for diagnosing the problem?

 

[PuffTheMagicDragon]

It could be that the cable is shorting. Does it pass through a pulpit tube or through a metal plate? If so, is it protected by a rubber grommet? I would examine the cable insulation for signs of chafe, especially in locations where it passes through holes.

 

[MagicalArmchair]

It could be that the cable is shorting. Does it pass through a pulpit tube or through a metal plate? If so, is it protected by a rubber grommet? I would examine the cable insulation for signs of chafe, especially in locations where it passes through holes.

The red and black cable on the right passes up through a hole in the deck, into the bottom of the pulpit and then up to deck level. You know what, you could be onto something. In the deck painting 'adventure', the deck was sanded multiple times - I could have nicked the cable at deck level? I'll investigate the when next down.

 

[sailorman]

The motoring nav lights on my pulpit I noted hadn't been working since my deck repaint. I assumed the terminals were corroded on the bulbs, so got to work cleaning them up one evening on our summer cruise. Tried them again after cleaning up, and no luck. I went below and took a look at the fuse, and boom, noted it had blown. I replaced the fuse, and snap, the lights dimmed for a sec, and the fuse blew again. That fuse just juices up the two nav nights on the pulpit, port and starboard. If, from the appliance side of the fuse, I disconnected the green starboard wire, the fuse no longer blew. If I unplugged port, and plugged back in starboard, the fuse would once again blow.

From the pulpit I unplugged the nav light, (fearing the light unit had a problem), replaced the fuse and the fuse STILL blew. Out of time by now, with the 1st mate accusing me of waking up our daughter sleeping in the fore-peak and it was time to come to bed myself, I grumpily gave up my fruitless diagnostics.

The below photo is directly under the pulpit in the anchor locker, the chocolate block attached to the ceiling. The green (starboard!) wire in the below, goes all the way back aft to the bottom of the fuse that keeps blowing. I can see in the below, the green wire looks corroded where it enters the hateful chocolate block. Do we think this could be the problem? My eletrickery skills are somewhat limited!

My next step is to replace the chocolate block and inspect\cleanup the wires here. Any other suggestions for diagnosing the problem?

The 3 core cable is that solid household cable or flex. if solid it is liable to fracture.
i would check as stated for a nick in the cable in the pulpit

 

[PaulRainbow]

99.9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999% likely to be a short to negative.

There should be no negative connection to the pulpit, so you'd have to have nicked both wires. Take the bulb and the fuse out and disconnect from the chocolate block. Test for continuity between the pos and neg to the light and then pos and neg from the supply. Whichever one has continuity will tell you in which section the short is.

 

[MonniotC]

Any corrosion in the cables is bad news as it introduces resistance and will cause the lights to glow dimly or not at all. It will not, however, cause the fuse to blow. The blowing fuse will be caused by a short-circuit.

 

[jwilson]

The original factory-supplied small 10 watt bow bicolour on my Jeanneau burnt to a dusty crisp the insulation on the wires coming into the light fitting: when I opened the light up the wires were to all intent bare, and could easily have shorted, though they hadn't, and the light was till working.

 

[MagicalArmchair]

Thank you all, that gives me some more vectors of attack on the problem. I'd like to get these working for the return trip from lovely Woolverstone and the pretty Suffolk coast.