Help please, wiring problem with masthead light

[DanTribe]

I have to admit that electrizicals is not my strongest subject and this has me stumped.
I have an Aquasignal tricolour / anchor masthead light. This uses 3 core cable, live to each lamp and common neutral.. Keel stepped mast so cable is disconnected / reconnected each year inside boat.This year when I switch on the anchor light the panel indicator for the tricolour lights, although the anchor light is on. Assuming I had mis-connected, I swapped cables but same result, except that now tricolour lights up. A meter indicates 12 V going up to anchor light but 8V returning down tricolour LIVE wire!
How can that be!
I assume a fault at the masthead and a trip up the stick is required, but it would be nice to know what I'm looking for.

 

[VicS]

poor connection on the common negative somewhere.

It could be at the top, it could be at the bottom it could be in the boat before the terminals for the mast wiring.

Before you go up the mast check at the bottom by disconnecting the mast wiring and connecting two bulbs in place of it.
A couple of 21 watt car stop or indicator bulbs would do nicely soldered onto some leads. If they dont work properly the fault is in the boat. If they do then go up and check the negative connections.
It's a plug in assembly I guess so may well be the neg connection between the light assembly and the base.
I bet you did not check and clean the contacts when you refitted the light assembly before stepping the mast.

A digital meter can have you running round in circles sometimes because they take so little current they will give a normal reading through a bad connection.

 

[DanTribe]

VicS
Thanks for your response. I've mostly done the checks you suggest. The connections in boat at mast foot are screw in "choc block" type connectors, not a plug, I've double checked and cleaned these.
With anchor light switch on and tricolour off, a test lamp between live & neutral lights normally and meter shows 12V.
BUT, and this is the bit I don't understand, a test lamp between anchor light live and tricolour live glows dully and meter shows 8V. [tricolour panel switch off].
All this is with the mast cable connected, disconnected the wiring acts normally, so I believe the problem is at the light. The anchor light works OK but I dont like the idea of the stray voltages.
It would be good to have an idea of what to look for before I go up because most of my thinking ability is used up by hanging on once aloft.

 

[jmh2929]

VicS
With anchor light switch on and tricolour off, a test lamp between live & neutral lights normally and meter shows 12V.
BUT, and this is the bit I don't understand, a test lamp between anchor light live and tricolour live glows dully and meter shows 8V. [tricolour panel switch off].
All this is with the mast cable connected, disconnected the wiring acts normally, so I believe the problem is at the light. The anchor light works OK but I dont like the idea of the stray voltages.

With the test light connected to the 2 positives and the achor light on, power will travel through the test and the tricolour to the neutral so giving 2 bulbs in series, therefore a lower voltage reading. The anchor light will be normal.
Switch all off and try doing resistance/continuity checks to ensure no shorting between circuits

 

[philip_stevens]

With the test light connected to the 2 positives and the anchor light on, power will travel through the test and the tricolour to the neutral so giving 2 bulbs in series, therefore a lower voltage reading. The anchor light will be normal.
Switch all off and try doing resistance/continuity checks to ensure no shorting between circuits

As said.

You should get a higher resistance between the two positive wires going to the two lamps - possibly 25w and 10w - in series.

You will then get two different resistance readings (assuming 25w and 10w lamps) between the positives and the negative in turn. This will prove the wiring to find the negative wire.

Go to your chock-block and ascertain the negative and two positives.

With all cables noted, connect and let us know what you now have.

 

[theoldsalt]

I think that JMH2929 has the answer.

Have you ever followed a car and noticed the indicator glowing when the brake light comes on or vice-versa. That is caused by a bad earth. One lamp is earthing through the other. So both lamps are in series.

So the fault is probably in the lamp unit at the top of the mast.

 

[VicS]

I think that JMH2929 has the answer.

Have you ever followed a car and noticed the indicator glowing when the brake light comes on or vice-versa. That is caused by a bad earth. One lamp is earthing through the other. So both lamps are in series.

So the fault is probably in the lamp unit at the top of the mast.

I would agree that the most likely place is in the lamp unit BUT from the symptoms originally presented the fault could be anywhere in the negative connection.

My suggestion to disconnect the mast wiring and substitute two test bulbs in its place was aimed at determining if the fault was within the boat or not.
It would be real PITA to climb the mast or lower it only to discover that the trouble was below somewhere!

The later results in posted in #3 I think indicate that the fault is at the mast top.

The OP does not indicate what version of the Aquasignal light he has. My old Tricolour was hard wired right to the bulb holder but there have been I think two versions of the Tri/white with quick fit bayonet fittings. My current tricolour plugs in but is retained by locking rings that are the invention of the devil. It's bad enough to fit or remove when the mast is down .. I'd not like to do it from a bosun's chair.

 

[DanTribe]

Thanks for all your replies.
I obviously need to do a bit more testing next weekend. I only had one test lamp available, so couldn't check both circuits simultaneously.
The light is an Aquasignal 40, the one where the lens fits with a quarter turn. The fitting itself is a push fit and clicks into place, I think the terminals are eccentric so can't be fitted back to front.
The light is fiited by the boatyard and they connect a battery to check the lights work before stepping the mast. Final connection is left for me to do.
The lights do appear to work OK [hard to check from deck level but can see Windex lit up] but the bit that bamboozles me is why a different panel indicator lights up, not the one switched on.

 

[VicS]

but the bit that bamboozles me is why a different panel indicator lights up, not the one switched on.

Ah! or rather Oh?
I'd not realised that the correct one did not light. I'd assumed they both lit.

Don't go up the mast just yet!

As far as you can tell both lights on the mast work correctly and at normal brightness.

Do they both still work at near enough full brightness if they are switched on together, or does the switching prevent you from doing that.

You said at the beginning that when the anchor light is switched on the Tri indicator lights. If you switch on the Tri does the anchor indicator light?

Not been doing any work on the panel?

Have to think a bit more .... busy at the moment fitting a new programmer on the heating system .. different connections to the old one!
Dont want to get the jobs muddled or every time I take a shower your nav lights will come on or something.


.

 

[Philthy]

At the risk of teaching granny to suck eggs, are you sure you know which wire is the common neutral?
As you can't blow anything on the masthead, using a 12v battery, and a 2 core cable, you can work out which cable is which for certain.
Just connect 2 wires, and see if anything lights up, then try the other wire. If both mastheads come on, you have managed to connect the + positive side of both lamps, and you know the remaining wire is the neutral.
Easier to find out this way if the masthead is ok, rather than stepping it/bosuns chair.

 

[VicS]

At the risk of teaching granny to suck eggs, are you sure you know which wire is the common neutral?
As you can't blow anything on the masthead, using a 12v battery, and a 2 core cable, you can work out which cable is which for certain.
Just connect 2 wires, and see if anything lights up, then try the other wire. If both mastheads come on, you have managed to connect the + positive side of both lamps, and you know the remaining wire is the neutral.
Easier to find out this way if the masthead is ok, rather than stepping it/bosuns chair.

If one of the positives is swapped over with the negative it will be pretty obvious.
One light will work Ok but instead of the other working you'll get the two in series so both on at much reduced brightness.

 

[DanTribe]

At the risk of teaching granny to suck eggs, are you sure you know which wire is the common neutral?
As you can't blow anything on the masthead, using a 12v battery, and a 2 core cable, you can work out which cable is which for certain.
Just connect 2 wires, and see if anything lights up, then try the other wire. If both mastheads come on, you have managed to connect the + positive side of both lamps, and you know the remaining wire is the neutral.
Easier to find out this way if the masthead is ok, rather than stepping it/bosuns chair.

Well I thought I was sure and I thought I had permed all combinations of 3 wires, but now I'm not sure of anything; a case of " the more I think, the more confused I get"!
It will have to wait until next weekend and I'll re-check everything and try again.
Another worry I now have, following VicSs earlier reply, is that when I switch on my navlights I may be reminded of him in the shower!

Thanks for all your replies, it's given me some pointers to look out for.