control panel fuses

John M.Sullivan · Post by **John M.Sullivan** » Jun 16th, '11, 19:33

This has got to be too simple: but my masthead light is out, the deck light (spreader light) is good the bulb is good, the wiring in the mast appears to be good; I've acutally been up the mast!....so I suspect a fuse or other issue at the control panel. The little white buttons aside the toggle switches are marked by various numbers that appear to be fuses (5, 15, etc). How do I get to them? I am thinking these haven't been checked since the boat was built in 1981. OMG, that's 30 years ago! Advice?

Maine_Buzzard · Post by **Maine_Buzzard** » Jun 16th, '11, 20:12

They may be circuit breakers, which will pop out when there is a short or fault in the circuit after the breaker.

Since one light works, you probably have a good ground on the light.

Get a 12v test light and start hunting. Clip one lead to the ground bus and poke the test tip on the circuit breaker terminals, then the switch terminals, and look for voltage there. (Switch should be on.) If that's live, go to the connection between the mast and the boat. It's either a terminal block or connector, check there for voltage.

One trick is to get a 40' length of wire, add a 2A fuse to it, then hook up a light bulb as a test light.

Clip the alligator clip to the ground bus, then look for the +12v on the mast connections and at the light. Mark those if they are good, or figure out why no +12v is making it to the mast light fixture.

If the +12V to the bulb is good, go back and hook the alligator clip to +12v from the battery (that's what the fuse is for). When you touch the test light to a good ground, the lamp will light up. (if you touch +12V, nothing happens)

Using the test lamp, look for the ground connection through the wire to the mast connector and then up to the mast light fitting. You should be able to find the other (unmarked) terminal for the light, and see that it's a good ground.

Half the time you have a bad +12v supply, half the time it's the return, and the other half of the time, both are bad.

Maine_Buzzard · Post by **Maine_Buzzard** » Jun 16th, '11, 20:29

Here's a mashup of what needs to be made.

<a href="http://s793.photobucket.com/albums/yy21 ... ircuit.jpg" target="_blank"><img src="http://i793.photobucket.com/albums/yy21 ... ircuit.jpg" border="0" alt="Photobucket"></a>

John M.Sullivan · Post by **John M.Sullivan** » Jun 16th, '11, 22:08

Thanks James - that's a great reply and you went to a lot of trouble to help me out. I'll report back on the results. You're a jewel.