Masthead wiring problem

okapi3 · #1 (**permalink**) 08-31-2011

I installed a new masthead LED tricolor/anchor light combo (Optolamp) on my 1988 PSC31. It uses the 2 existing wires from the old anchor light and a polarity reversing switch to switch from tricolor to anchor light. So far the tricolor works fine by flipping on the old anchor light switch at the main panel but I have run into a snag wiring the polarity reversing switch. I know exactly how to wire it, thanks to a friend who is an engineer, but in order to to so I need to find the negative ground for the masthead light and therein lies the problem. I turned the tricolor on and disconnected each black wire from the DC negative bus one at a time looking to see when the masthead light went off (which would indicate that was its black wire) but it never went off! Grrr. Apparently the masthead is grounded somewhere else. I wrote to Thumper and his guys said they thought the masthead was grounded to the main panel. I then used my ohmmeter and checked resistence between the mast and the DC negative bus and lo and behold there was low resistence, indicating the mast itself is somehow in circuit with the boat's circuit ground, which is why the light never went off when I disconnected the black wire from the panel. so what do I do now? Is the mast supposed to be connected to the circuit ground or is that due to a short inside the mast? And how do the wires from the mast get to the panel anyway? I could fish a new ground wire through the mast but I don't know how to get from the base of the mast to the panel. sorry about the long post. I am at the boat now for another 5 days so hopefully can get this problem solved. Thanks!

niftynickers · #2 (**permalink**) 08-31-2011

I don't know about the 31 but on my 37 the mast is stepped into a shoe on deck that is grounded to the Dynaplate.The Dynaplate is also strapped to the engine block and to the negative buss.All mast wiring goes thru the shoe and down thru a wire chase in the compression post to the bilge and then to the panel.For your purposes it sounds as tho the mast is the negative conductor.

okapi3 · #3 (**permalink**) 08-31-2011

So the mast is grounded to the dynaplate, but should the wiring for the masthead light be grounded to the mast also, or just run down through it? .

BluesHarp · #4 (**permalink**) 09-01-2011

I might be wrong, but if your mast is carrying the negative, then you will not be able to use a polarity reversing switch. You sure do not want to send a positive charge into your mast if the mast is grounded to your negative bus. You will have to run new wires to your lights, and revise your plan.

niftynickers · #5 (**permalink**) 09-01-2011

Since the dynaplate is also connected to the negative buss your mast is the same potential as the black ground wires.The light housing itself may be connected electrically to the mast and thus to the neg buss.That would explain why the light stayed lit even tho you disconnected the black wires.If you can isolate the light assembly electrically from the mast then your polarity reversal might work.All of this of course is guess work.
good luck,
Dianne and Chuck Burke S/V NiftyNickers C37 #139

okapi3 · #6 (**permalink**) 09-01-2011

Thanks both of you for your good advice. Yes, I think I will end up having to fish a new wire down through the mast after all in order to isolate the light assembly from the mast as you said. Too bad--I thought this was going to be a simple "Plug 'n' Play" installation. I will let you know how it turns out.

By the way, the Optolamp is a great unit, made in Brazil, sells for much less than the competition , and uses about 1/14th the amperage of three incandescent running lights. Makes a huge difference on an an ocean passage!

Paul

niftynickers · #7 (**permalink**) 09-02-2011

If it involves a boat ITS NEVER EASY!

good luck,

Dianne and Chuck Burke S/V NiftyNickers C37 #139

okapi3 · #8 (**permalink**) 09-07-2011

I got the polarity-reversing switch wired and working! Here's the story (exciting part is at the end!). There is a small plate on the SB side of the base of the mast with access to internal mast wiring. Turns out the ground for the masthead light comes down separately but then at the bottom of the mast gets combined with the ground for the steaming/foredeck light combo before going through the compression post to the panel so is not usable for the purposes of polarity reversing--must be isolated from all other grounds. The mast wires were all taped together into an impenetrable mass of black electrical tape and siliconed into the hole going through the deck. There was not enough slack to do anything with it or fish anything down the compression post so I ended up drilling a hole in the base of the mast and another hole in the deck close to the mast and splicing a new ground wire from the masthead light and running that out the base of the mast, down through the deck, above the headliner, through the hanging locker to the control panel.

Once I got those wires more or less in place and watertight, we left to go sailing, planning on wiring the switch at anchor just before nightfall. LESSON #1 LEARNED: ALWAYS TURN OFF BATTERY POWER BEFORE WORKING IN CONTROL PANEL! Did not do that, and as I was connecting a new black wire between breakers and negative bus it shorted with the hot wire coming in which instantly incinerated both wires and started a small white hot fire in my control panel. I had the fire extinguisher at ready but fortunately didn't need to use it. The fire did some superficial damage to insulation of some adjacent wires and scared the pants off my wife and me but after replacing the 2 charred wires (using flashlights for illumination since was already dark) we were back in business and we had a working anchor light that night.

Once back at marina, I carefully turned battery selector switch to OFF to clean up wiring mess, but was once again surprised when my sweaty hand touched the 120V bus and got a good jolt. LESSON #2: Always disconnect shore power before working on control panel! I really live my motto below: bad judgment>>experience>>good judgment.

niftynickers · #9 (**permalink**) 09-08-2011

John aka Sparky,

You have had a crash course in electricity 101.You are also very honest as most people that I know would never admit to these misadventures.
Happy to hear that your new light works well and that you figured out the mast wiring.Sorry to hear about the smoke and excitement.The DC makes heat and smoke but the AC is really dangerous as you've learned.Thats the stuff that kills.
Goodluck with your more cautious electrical adventures.

Dianne and Chuck Burke S/V NiftyNickers C37 #139