(engine related) electrical mystery

pegasus1457 · #1 (**permalink**) 07-19-2009

I have been postponing solving my tachometer problem (earlier post) where a non-contacting optical tach was reading 2X higher than my tach on the engine panel. I finally got around to doing something about it. I know there is a multi-position switch on the back of the tach to account for alternators with different numbers of poles. Unwilling to break the silicone seal on the engine panel, I tried to change the switch setting by the braille method. I turned what I thought was the switch and it disappeared, leaving a keyhole shaped void in the back of the tach.

I had been listening to the FM radio on the cockpit speakers and suddenly the radio turned off. Investigating I found the house panel was dark. When I turned on the main breaker I read about 2V on the house panel's voltmeter.

I was sure I had jostled something in the battery box, so I re-tightened all connections. No joy. While I was doing good things in the battery box I spied the missing "switch." But it wasn't a switch that I had turned, it was a little module with a light bulb in it. I finally removed the engine panel, silcone and all. When I replaced the little light bulb suddenly all the problems with the house panel disappeared. And while I had the panel out I made the tach adjustment that I had started out to do ...

So the long story is the background to my question: what does that light bulb have to do with the house panel? I know that there is another bulb somewhere that provides exciter current to some alternators. But it is not this bulb (I don't think) and even if it was, I still don't understand the connection to the house panel.

Can anyone enlighten me?

scottyt · #2 (**permalink**) 07-19-2009

my boat has a small light on the top of the dc panel, it acts like a night light for the breakers. its basicly a courtesy light so you can see what your turning on or off when its dark

pegasus1457 · #3 (**permalink**) 07-19-2009

So does mine, but the panel in question here was the engine control, in the cockpit, not the house (DC) panel. And the tachometer adjustment is in back of the engine panel, deep in the bowels of the starboard cockpit locker ...

Quote:

Originally Posted by scottyt

my boat has a small light on the top of the dc panel, it acts like a night light for the breakers. its basicly a courtesy light so you can see what your turning on or off when its dark

scottyt · #4 (**permalink**) 07-19-2009

i wonder if it was a replacement for the stock light in the tach then, mine has a light in the tach. or maybe just a light to be able to see other stuff on the panel