Fault finding

Ms. Bettencourt has been having some problems with her navigation lights. Finding and fixing these faults teaches many lessons in logic and troubleshooting.

For example, the two LED lights atop the mast stopped working. Logic, assisted by expert advice, led down this torturous rathole:

• Must be the LEDs, though both failing at the same time is unlikely.

• Perhaps it is the wiring inside the mast? Remove mast and bring it to the 12-volt power supply on the shop bench. Apply power. LEDs light up. Wiring OK. Re-install mast.

• Think about it for a week. Involve two experts who agree it could only be the switch. Order $8 switch that winds up costing $31 due to rush air shipment from California. Install new switch. No change.

• Think about it for another week. One expert says wiring polarity is reversed. Logic says that since the lights worked last summer, how did polarity get reversed? A ghost technician? 

• The other expert says it's a  fault in the wiring between the switch and the fixture.

The instrument to the left, by the way, is a very old 12 volt power supply given to me by a friend about 15 years ago. It's a handy tool for on-the-bench troubleshooting.







After another week, I begin to close in on the obvious: The two quick-connect fittings for the mast -- the male fitting on the cord from the mast and its mate in the top of the boat over the windshield. Removing the weather covers on both fittings revealed nothing obvious. But, since all six wire ends were exposed and accessible, why not make sure?

I removed each wire, one at a time, and tinned them with solder, then restored and re-tightened each connection. And it worked -- kind of.

The two masthead LEDs together comprise the anchor light, and they burned in response to that position at the switch. The other switch position, for running lights, is supposed to illuminate the forward masthead LED, the port and starboard running lights and the stern light LED.

Whoa! No stern light. So, here we go again.

• Check to see if there is 12 volts to the stern light fixture. No. 

• Check fuse. OK. 

• Check splices between switch and fitting (remove part of aft cabin floor and hull liner to do this). Remove 1972 splice block and make new connections. No joy.

After a few more days, I remove the stern light fitting and take it to the bench in the shop. Application of 12 volts from the bench power supply directly to the LED gets zero result. Hah! Bad LED! Locate, order a new LED.

The next day, with nothing else to do while awaiting the new LED, I put an incandescent bulb in the stern light fitting as an additional test. No light! So, I disassemble the entire light fitting and in the process discover the positive contact is badly corroded. Fix that. Clean the other contact for good measure, reassemble and

...the incandescent light works. (That's the dead LED in the foreground to the right of the light fixture).








So now, I have reinstalled the fixture, reconnected the various splices and reassembled the aft cabin hull liner and floor panels.

Logic tells me that, when the new LED gets here, it will work in this fitting too.







We'll see. I am not too confident. My kind of logic has proven quite circuitous.