Only one brake light, no voltage at the other. Marker lights work instead

[Danny69]

Hi all,
Weird one this, only the offside brake light on my 2003 coachman amara is working. No voltage at the nearside bulb.
The marker lights on the offside are not coming on with the other lights but are coming on when I brake.
I am sure this has only occurred since I changed my tow car and have had new tow bar electrics fitted but I can not understand how this could happen. Only one wire feeds both brake lights on the caravan afterall? I don't want to call the tow bar company out unless it is likely that the problem really does lie there.
Any help would be welcome as I am going round in circles

 

[EW1999]

Hi all,
Weird one this, only the offside brake light on my 2003 coachman amara is working. No voltage at the nearside bulb.
The marker lights on the offside are not coming on with the other lights but are coming on when I brake.
I am sure this has only occurred since I changed my tow car and have had new tow bar electrics fitted but I can not understand how this could happen. Only one wire feeds both brake lights on the caravan afterall? I don't want to call the tow bar company out unless it is likely that the problem really does lie there.
Any help would be welcome as I am going round in circles

a little not enough data. Are you using one plug or two (7 or 13 pin socket on the tractor)?
I suggest starting with a tractor. You only need a 12V bulb and two wires.
Turn on the bulbs on the tractor in series and check which socket contacts make the bulb burn. then check the contact numbers with the diagram. I can lay out the scheme when I find out how many sockets are used. or the diagram is available on the internet.
further more)))

 

[Danny69]

thanks, I have a 13pin socket on the car which using a splitter feeds the two 7 pin sockets on the caravan.
I did a quick test on the 13 pin socket with a volt meter between pin 3 (earth) and 5 6 and 7 and it seems only 7 is producing voltage. Either when I turn on the lights or press the brake!!

 

[EW1999]

thanks, I have a 13pin socket on the car which using a splitter feeds the two 7 pin sockets on the caravan.
I did a quick test on the 13 pin socket with a volt meter between pin 3 (earth) and 5 6 and 7 and it seems only 7 is producing voltage. Either when I turn on the lights or press the brake!!

Well, that's probably the answer. Disassemble 13 contacts and see. maybe they are rotted or there are blown fuses between the contacts in the socket and the lamps of the car.
the seventh pin is however intended for the dimensions of the left side.

 

[Danny69]

Well, that's probably the answer. Disassemble 13 contacts and see. maybe they are rotted or there are blown fuses between the contacts in the socket and the lamps of the car.
the seventh pin is however intended for the dimensions of the left side.

It was brand new last year. I think I will phone the firm that fitted it next. Thanks. I will let you know the outcome

 

[Woodentop]

The OP says no voltage on the nearside bulb socket, but how is he measuring it? If it is between the socket terminal and the socket common earth plate, and the earth on that common plate has come adrift then he will not read voltage.

Before going digging into wiring and sockets I would do more careful checks around the lighting plate connections.

For the record the brake lights as correctly stated have one feed (hence why there is unlikely to be a tow socket problem as the O/S bulb works) BUT the tail lights and side markers have two feeds, one to the offside lights and one to the nearside PLUS the registration plate lights.

 

[EW1999]

​ Before going digging into wiring and sockets I would do more careful checks around the lighting plate connections. the lanterns did not take part in the check. there was no talk of malfunctioning of the tug lights. we must wait for a new question from the applicant. do not touch the caravan prematurely.

 

[Dustydog]

The marker lights on the offside are not coming on with the other lights but are coming on when I brake.
Sounds very much like a poor earth . The current is seeking an escape via the wrong route🤪

 

[Danny69]

The marker lights on the offside are not coming on with the other lights but are coming on when I brake.
Sounds very much like a poor earth . The current is seeking an escape via the wrong route🤪

That's what I thought at first. But the earth seems okay on the back plate as the other lamps on the nearside cluster work fine. Also I ran a wire from the working side live to the other side and then it lit up.

 

[Dustydog]

Have you tried the same test but with the brake lights kept on?

 

[Danny69]

Have you tried the same test but with the brake lights kept on?

Yes they were kept on when I did it. They wouldn't have lit if the brake wasn't pressed

 

[EW1999]

I think there is not enough photo of the opened trailer socket

 

[Danny69]

A quick update. I got a friend to connect his 7 pin socket to my caravan and all lights worked as the should .
So presumably the fault can only lie in the 13pin socket wiring on my vehicle or the splitter / adaptor which converts the single 13 pin to two 7 pin sockets. If I can prove it isn't the splitter I can get the the guy that fitted towbar to come back.

 

[EW1999]

It's not hard to prove. Each connector must match the diagram. It is enough to have one light bulb and two control wires. Or you can use a special tester.

 

[Danny69]

Thanks yes, I will test the cars 13 pin socket again and the splitter. It is just that he will charge £25 call out if it isn't his fault.