Indicator problems help please!!!

[Noel1]

Hi Forum, I have a problem indicator on my caravan, changed bulb no good, checked if voltage was coming through wire via a multi-meter and it is but when I insert bulb power disappears! Have checked correct voltage and wattage of new bulb (12v/21W).

Any pointers greatfully apprecaited.

Regards

Noel.

 

[rob_jax]

Noel,

Quite a few things to check becuase it sounds as if you have a high resistance somewhere in the wiring. And as soon as you try to draw almost 2 amps (21 Watts), the voltage decays away.

1. Remove the light fitting and check that the electrical contacts are in good condition and make a good springy contact with the bulb.

2. Measure the resistance of the 21 watt bulb with the multi-meter. Check and compare the resistance with the bulb in the light fitting. If the resisitance is much higher - then it's a fault in the fitting.

3. Check the resisitance at the caravan plug - if it's much higher than that of the bulb - then it's a problem with the wiring.

4. Check the wiring in the socket and plug - look for green corossion to the copper wire - and make sure that the wire hasn't been cut through by the screw

5. Check the junction box - trace the 12N wiring - possibly under the caravan - and check that all the wires are OK

Robert

 

[Essexeddie]

Bad earthing!

 

[JeremyClarksson]

I don't think it is bad earthing and would agree with RJ on what he says.

If it was a bad earth you would expect the voltage to stay the same and the bulb not work.

More likely to be a bad connection in the L(switched) feed for the bulb.

Loosely explained lets say you have no bulb in the circuit and you have a high resistance connector - you will get 12V at the bulb socket because no current is flowing through the bulb, no volts drop across the high resistance connector because the biggest resistance is where the bulb should be - hence 12V across the bulb contacts.

With the bulb plugged in the largest resistance in the circuit is now the bad connection, so close to 12V across the connection and little or no voltage across the bulb.

.....and there is the solution to the problem, keep going back along the L feed until you find the connector with the volts drop across it or if car electrics disconnected use the meter on the resistance range to find the high resistance.

 

[lefrog]

Noel

we had exactly the same problem turned out to be the pins in the 12n connector (just prise them open a little with something thin)eg:-screwdriver blade.thats on the socket & connector.

tom

 

[AnnM1]

We had the same problem with our brand new 2007 caravan!!! We took the offending light fitting off and tried replacement bulbs, but this didn't work for us either.

Finally, after about half an hour we decided it could be a spec of corrosion preventing contact. We used an emery board (fine side) on the contacts, followed by a tiny bit of WD40 replaced the original bulb, and it worked. We have had no further problems.

 

[rob_jax]

If people find WD40 work for them, then fine.

But you'd be better off using a silicone spray for electrical connections - it has a much longer "residence time" and so protects for far longer - and won't swell rubber seals either.

And as someone in the petrochemical industry - WD40 is just odourless paraffin oil - like Esso Blue paraffin. But supplied in a handy spray can.

Robert

 

[Noel1]

To all off you a big THANK YOU. Last night the problem was resolved. A bad earth was the problem. This forum has renewed my faith in others being able to help others (I mean this sincerely). My wife and two children are heading south from our home in Inverness (in a few days) to enjoy Culzean Castle. If I didn't get this fixed I wouldn't have been going. So once again thank you. Rob_ tried easiest first, thanks for tips on MM.

Regards

Noel (Eriba Nova)

 

[JeremyClarksson]

One up for Essexeddie, it did not sound like a bad earth to me but proves it is always something worth checking!

 

[rob_jax]

Both of you were right - it's a fault in the wiring - and it could be anywhere in such a simple DC circuit and have the same effect. It doesn't matter to the bulb if the resistance is before or after - it won't work either way.

Robert

 

[JeremyClarksson]

Because of the symptoms I thought and said that the fault was more likely in the feed part of the circuit, however happy problem solved.

Thinking about it a bad earth would have given the same symptoms mentioned in the first post if the measuring was being done using a good earth.

 

[ProfJohnL]

Hello Noel,

I am glad you have resolved it.

I have a question for you though, Can you tell us where the 'bad earth' actually was please.

My reason for asking is that if a caravan has a bad earth, it will normally affect more than just one bulb, as the earth is usually shared by all the bulbs in the light fitting, and ultimately by all the lights.