Jump to content

Tow-bar Electric Problem


Recommended Posts



Can anyone help please, I have just connected my "A" frame to the car and Motor-home and the indicators won't work, I tried just connecting the towing board to the plug on the motor-home tow-bar and the running lights work together with the brake lights, but the indicators both left and right don't work, they do on the motor-home .


I don't know if its relevant but I also don't get the louder indicator noise in the cab, its a 7 pin plug, any advice or suggestions would be very welcome.


The wiring on the car is completely separate when thy fitted the "A" frame they ran a cable fixed to the underside of the car with separate plugs at either end so I have to connect the tow-board to a plug in the boot and the "A" frame to a separate plug under the bonnet and the other end to the motor-home tow-bar.


As I mentioned above I have connected the Tow-Board direct to the Motor-Home tow-bar plug so I think that should rule out any problems with the tow-car ?




Link to comment
Share on other sites

Guest JudgeMental

if its a fiat did they know what they where doing when they fitted plug? *-)


Fiat can bus system needs a relay OR expensive Fiat wiring thingamajig,,,,,

Link to comment
Share on other sites

You need to 'test' your plug in the Motorhome First . Do you have a digital Volt meter ? or any kind of 12v tester ?


This is the wiring diagram, the top one is the one you use.




If you don't understand it, and have no test equipment (as above) you need to see a professional.



from your description it sounds like you have a bad earth connection,but without testing it ?

Link to comment
Share on other sites

You may have two slave relays for the trailer indicators and these have lost a supply perhaps. You need a sparkies brain and a multimeter.


The connections for the standard 7 pin socker are :-

ISO 1724N

Pin Code Duty Current (amps) estimate Colour

1 (L) Left hand indicator 2 amps yellow

2 (54G) Rear Fog lights via switch on dash. 8 amps blue

3 (31) Chassis return 18 amps white

4 ® Right hand indicator 2 amps green

5 (58R) Right hand Tail lights 1 amp brown

6 (54) Stop lights 4 amps red

7 (58L) Left hand Tail lights 1 amp black


The connection for the extra 7 pin connector for caravans is :-



1 (L) YE Reversing lights

2 (54G) BU Caravan batty charge supply (only when engine running)

3 (31) WH Chassis return for pins 2 & 6

4 ( R ) GN Interior lights, water pump etc Permanent supply

5 (58R) BN Unused

6 (54) RD Fridge supply (only when engine running)

7 (58L) Unused.



If you have the European 13 pin connector then the pin out is :-


An “all in one” connector that serves the job of both our “N” and “S” connectors.

ISO 11446 EN 1648-1 DIN 72570


Pin 1 Left hand direction indicator

Pin 2 Rear fog light

Pin 3 Common return for pins 1,2 & 4 to 8

Pin 4 Right hand direction indicator

Pin 5 Right tail lamp, side lamp & number plate lamp

Pin 6 Stop lamps before

Pin 7 Left tail lamp, side lamp & number plate lamp

Pin 8 Reversing light

Pin 9 Continuous power supply

Pin10 Power supply controlled by ignition switch for charging caravan battery.

Pin 11 Return for cable number 10. (Not Allocated before Oct 98)

Pin 12 Coding for coupled trailer. Linked to pin 3 in plug. (Not Allocated before Oct 98)

Pin 13 Return for pin 9 ( Return for pins 9 - 12 before Oct 98)

Information source dated October 1998


Hope that helps a bit.


Good luck




Link to comment
Share on other sites

But, before it gets too complicated, have you inspected the connections on the 7 pin towboard plug?


Also, silly as it may seem, have you inspected the lamps, and their connections, inside the towboard indicators?


Final thought: is the socket on the van of 7 pin, or 13 pin, variety? I seem to remember reading a while back that there had been some change to the wiring of the 15 pin sockets and that, consequently, the wiring of 7 pin plugs, where these were being used, would need to be changed.


You may find this link instructive: http://www.caravanclub.co.uk/media/1022790/towbar-wiring-mo.pdf, as Ray's sheet is from 2005, and a lot changed in 2008.

Link to comment
Share on other sites

I am afraid to point out that Rays sheet is wrong regarding the split charge relay. If it is wired as shown the main split charge fuse will blow when the engine is cranked because the ignition switch will be turned On and the relay will be energised. Consequently the leisure battery will try and contribute towards the engine starting current. The positive coil supply for the split charge relay must come from the alternator D+ terminal because this is not positive until the engine is running and the alternator is charging.







Link to comment
Share on other sites


Best guess is that a supply fuse (or connection ?) has failed on the supply of electics to the indiactor circuits. ie the live feed that powers the trailer indicator lights, not the actual m/home lights which only activate the relay.


You will have to follow the socket wiring back to the source, which may be mounted in the dashboard some where.



Link to comment
Share on other sites

Or you could just be very unlucky and both bulbs in your 'trailer' board have failed at the same time.


Remember the old adage, always start with the basics, and in this case the bulbs are the first item I would check.


Failing that I would go with Tony's comment above about looking for a fuse.

Have you tried contacting whoever fitted the towbar (if you can still contact them) to ask if they know if a fuse is fitted?



Link to comment
Share on other sites


This topic is now archived and is closed to further replies.

  • Create New...