Compass light circuit

[seabreeze384]

This seems to be my week for posting questions on the board. My compass light hasn't worked in some time and I really didn't worry too much about it since I don't sail at night. When it quit working is anyone's guess. Last week I decided to try to fix it. Bulb works, but no power at the bulb. Fuse blown. Install new fuse, blown fuse again. Hummm. I looked at the wiring diagrahm which shows 1 wire coming from the fuse to the hot side of the switch and one wire from the load side of the switch to the bulb. Then 1 wire from other side of bulb to ground. Simple, right? Nothing is simple on a boat. My as built wiring has 2 wires attached to the load side of the switch not 1 as the wiring diagrahm shows. Both as built wires go into the bilge and vanish. I am unable to find where they go. One obviously must find it's way to the compass light (it did work once upon a time). I can not imagine what the other wire is connected to. Since the fuse has been blown for some time I would hae thought I would have noticed something not working. But I haven't. As a fix, I ran new wire from the load side of the switch to the compass light and back to ground. All works well. But I am wondering where that mystery 2nd wire goes and why there is a short that keeps blowing fuses. My Morgan was built in 1984. The switch is the one in the cockpit (middle of 3) next to the engine instrument panel. The wiring is factory original as far as I can tell. The short could be in either of the 2 load side wires since I was unable to trace either to a load or terminal block. They must come up out of the bilge somewhere but I could not trace them successfully.

 

[matt_fahey]

Rick -

When wiring a compass, you need to use twisted wires, or else you'll have a electro-magnetic field right near the compass - not good! Edson sells some at a pretty expensive price, or you can simply twist your own.

When I re-wired my boat 2 or 3 years ago, I removed all "mystery" wires. There was an orange wire running from the engine panel down to the bilge, if memory serves. There's a bilge switch on the engine panel (along with a blower switch and a compass light).

Morgan made a great boat, but I was les-than-thrilled with the wiring job they did. When you rip out all the old to replace it with all-new, you find out that they used thick-stranded un-tinned wire, put the AC and the DC in close proximity, used black for "hot" AC wire and black for negative DC wire (which can confuse - and kill - the ignorant), and didn't provide a whole lot of diagrams on where the wires ran. As I re-wired the boat, I got comfortable with what the code required, and kept away from shortcuts that might save on materials, but make it difficult to understand what wires go to what devices.

Obviously, the code was a lot more lax in the late 70's, and Morgan didn't anticipate owners would need to gain access to wire runs... but so did many other boat manufacturers in those days.

 

[jose santin]

Another trick to avoid stray magnetic fields is to use a red LED instead of a bulb, it will consume less current thus a smaller magnetic field.

 

[larryhume]

Matt,
I think that reality is accurate in your last sentence. That's how it was done then. I have no complaint, the wire has lasted 30 some odd years.
Other than bilge pump rewireing and installing a new charger I have not had to do any rewireing on Southerly. I think that if I kept Southerly in a slip, rather then a mooring I would have rewired the AC to update to todays code.
But then I think about my house. Built in 1975 to code. We have never had any problems. I would bet that it would not meet todays code.
The bottom line is if either the boat or the house wires were not delivering the electric volts current and amps that they should, or the insulation looked suspect, I would rewire, tinned and to todays code. Or better.
Larry