Testing mast electricals, mast down

[webcraft]

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I need to test the steaming light and tricolour on Avy-J's mast. I have a 12 volt battery (the new engine start battery, fresh from Halfords and still to be fitted)

The lights are connected with a single 3-core cable at the moment with a three pin deck plug at the bottom. I am assuming that if I apply 12 volts across the common earth and one of the positives one of the lights should come on, and that the other light will come on when I swap a lead from one postive terminal to the other. But I have a few queries, never having done this before:

a) Am I correct in my assumptions?
b) How can I test which is the common earth and which are the two positives? Continuity test with multimeter?
c) Any particular size of wire needed from battery terminals to deck plug terminals ? I assume any lighting-size cable will be sufficient?

- W

 

[sgr143]

I needed to do something similar when my mast was down this winter, owing to the complete dog's breakfast that the previous owner had made of the wiring. Use a length of wire a bit longer than the mast to extend one of the probe wires from the multimeter, then you can use one of the "ohm" settings to see which plug pin connects to what at the mast head. You could of course also do it by dismantling the plug and checking the colours of the insulation around each wire, but using the meter will also tell you whether the connection is in good, low resistance, condition.

 

[BabaYaga]

.
I need to test the steaming light and tricolour on Avy-J's mast. I have a 12 volt battery (the new engine start battery, fresh from Halfords and still to be fitted)

The lights are connected with a single 3-core cable at the moment with a three pin deck plug at the bottom. I am assuming that if I apply 12 volts across the common earth and one of the positives one of the lights should come on, and that the other light will come on when I swap a lead from one postive terminal to the other. But I have a few queries, never having done this before:

a) Am I correct in my assumptions?
b) How can I test which is the common earth and which are the two positives? Continuity test with multimeter?
c) Any particular size of wire needed from battery terminals to deck plug terminals ? I assume any lighting-size cable will be sufficient?

- W

If this type
https://www.force4.co.uk/force-4-2-pin-3-amp-waterproof-plug-socket.html
the negative/ground is usually the slightly coarser pin.
If the lights are incandescent, which wire is the common negative is really decided at the junction where the three core is split to supply the two lights.

 

[VicS]

.
I need to test the steaming light and tricolour on Avy-J's mast. I have a 12 volt battery (the new engine start battery, fresh from Halfords and still to be fitted)

The lights are connected with a single 3-core cable at the moment with a three pin deck plug at the bottom. I am assuming that if I apply 12 volts across the common earth and one of the positives one of the lights should come on, and that the other light will come on when I swap a lead from one postive terminal to the other. But I have a few queries, never having done this before:

a) Am I correct in my assumptions?
b) How can I test which is the common earth and which are the two positives? Continuity test with multimeter?
c) Any particular size of wire needed from battery terminals to deck plug terminals ? I assume any lighting-size cable will be sufficient?

- W

a) yes

b) If they are filament bulbs by measuring the resistance between pins two at a time. One pair will have about twice the resistance of the others or the sum of the other two if not the same power. Those will be the two positives. (Expect the common negative to be the larger diameter pin as suggested or offset.
If you get two similar readings of a few ohms and one double, or equal to the sum of the other two, that then it pretty much indicates all is OK

If they are LEDs I guess just by trial and error.

c) yes ordinary 6 amp flex will be OK

BUT THE BIG RISK IS SHORTING THE BATTERY. If you go on to actually testing them be very careful. A fuse in the battery connection might be a wise precaution

 

[[70521]]

Does your multi-meter have the ability to "Buzz" when you have a circuit? If so use that.

 

[paulieraw]

If you are just testing to see if there is a circuit thern continutiy test if you haven't then your reading will show it. If you are looking to see if you have a short, then you need to do some math, but first test the system works.

 

[MoodySabre]

I did exactly that after fitting a new LED steaming/deck light a few weeks ago with the mast down. I have a 12v transformer that has small croc clips, a very handy thing.

 

[tross]

Just put the battery across two of the wires - if two bulbs light then the unconnected wire is the ground. If one bulb comes on then you jut have to try one of the other wires - if two bulbs comes on... If the other bulb comes on then you have identified each wire.

 

[Daydream believer]

Whilst you are at it I would scrap the plug & fit a deck gland then take the wires through the deck & join to the inner wires under the deck in a dry position Do this in a junction box on a bulkhead or within the head lining.
Plugs & sockets get water in them and can be a real pain in the rear