Interesting that it only blows the breaker when screwed into the (aluminum?) toe rail. Let us know if the nylon screws solve the short. If so, you definitely have a short in some wiring running in the channel at the deck/hull joint that is touching a bolt causing a short circuit through the toe rail.
Alternatively, how old is the breaker? The wiring? Original to the boat? As a marine electrician, I don't even bother diagnosing equipment >40 years old. My rate is more expensive than replacing old parts with new ones... On Thu, Aug 11, 2022, 8:11 PM Randy Stafford via CnC-List < cnc-list@cnc-list.com> wrote: > Hello Listers, > > I’m in need of your sage advice or at least hypotheses on an electrical > problem. > > Here’s the background. Late last season my starboard running light bulb > burnt out. It was a simple incandescent bulb, and the fixtures were > probably original. So I thought hey, why not replace all three running > lights with LEDs. In the process of doing that, I accidentally dropped the > port fixture’s dome cover to the bottom of my slip (no chance of recovery; > zero visibility). So, shit. I buy three new fixtures which have the same > hole pattern as the old ones but of course take different bulbs so I had to > buy LED festoon-style bulbs too. What started out as a simple $1.50 bulb > replacement turned into a $150 project. And of course the new fixtures’ > bases are thicker than the old, so I had to get longer stainless screws and > drill and tap deeper holes in the stemhead casting. > > Well, after getting everything back together I discovered the running > lights circuit is blowing its fuse within seconds of switching it on. But > only when the dome covers are screwed on to forward fixtures (the new stern > fixture including dome cover screws into the teak taffrail and causes no > problems). I’ve now isolated the misbehavior to screwing the forward dome > covers on. If I leave the covers off, the LED bulbs burn all night. I can > press down on the fixtures and twist the LED bulbs around no problem - none > of that causes any contact that shorts the circuit. If I put the covers on > but don’t screw them down, the LED bulbs burn all night. But as soon as I > screw those forward covers down, blown fuse. > > I’ve pulled the fixtures and looked carefully again at all the wiring, > including in the forepeak under the deck. There is no pinched wire or cut > insulation. The wiring to the fixtures goes through different (and much > bigger) holes than any of the screws do. My heat-shrink butt connections > are tight. As a short-term solution I just bought some nylon screws to > hold the covers down. I haven’t tested that yet, but hopefully it works. > > Meanwhile I’m pretty mystified. Any theories? > > Thanks, > Randy Stafford > SV Grenadine > C&C 30 MK I #79 > Ken Caryl, CO >
