Hey Randy, Strange problem. Something is creating a dead short to blow the fuse. The lights have a ground and one hot wire each. I'd be curious if the dome has a metal ring and looking to see if the hot bulb tab is touching the metal ring or the dome screw. You can insulate it with electrical tape or some liguid nylon paint made to isolate electrical terminals.
https://www.walmart.com/ip/Plasti-Dip-Liquid-Electrical-Tape/16888975?wmlspartner=wlpa&selectedSellerId=0&adid=22222222222009616975&wmlspartner=wmtlabs&wl0=e&wl1=s&wl2=c&wl3=10356703939&wl4=pla-1103084903071&wl5=&wl6=&wl7=&wl10=Walmart&wl11=Online&wl12=16888975_0&wl14=liquid+nylon+coating+electrical+tape&veh=sem&msclkid=4568518b85b11293c354337e43110c92&gclsrc=ds Chuck > On 08/11/2022 8:10 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
