New towbar electrics issue

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bodminman

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Hi there,

I’ve had a Towbar fitted to my Nissan Juke so that I can tow our little caravan about locally.

The issue is that when the caravan is plugged into the socket on the car, the lights on the caravan don’t work on it. Ie when the indicators etc are going on the car they’re not going on the caravan.

I have had 3 people with towbar a plug the caravan in and they work absolutely fine.

The garage response is that the Towbar electrics work fine when plugged into the MOT tester.

Anyone got any experiences with sort of thing?

Thanks
 
So, everything works except your caravan, I'd start by stripping down the caravan's plug. Is it a 12N plug?
 
Everything works when other vehicles are connected.

When my vehicle is connected nothing works.

The caravan has a 12n plug but Towbar has 2x 7 pins. I have harness to connect the van to the car. The harness is is fine as that’s been used to connect to 2 of the other vehicles. One vehicle had a 12n and that worked fine too.

The only think that doesn’t work on the caravan is my vehicle. :(
 
Sorry, I didn't read it very well. Then, it looks like the fault is with your new towbar socket. It's easy to test them, here's a picture of how it is wired.
 
bodminman said:
The caravan has a 12n plug but Towbar has 2x 7 pins.
Click to expand...

One is the original 12N black socket, the other the 12S grey supplementary socket, both 7pin. The 12N was the original basic socket, to supply the road lighting. The 12S, took things a stage further, with charging the caravan' battery, plus a supply for a fridge.

12N + 12S have no been superseded, by a single 13pin Euro socket, so I'm surprised that anyone might fit 2x 7 pin sockets, these days?

Testing whether a 12N socket is working correctly, is fairly easy, it just needs a 12v 18w brake light bulb, connected to a couple of wires, plus a diagram of the 12S socket.

Diagram


Connect one wired to pin 3, the other to what you are testing - pin 3 and pin 7, with left indicator on car flashing, your test lamps should flash.

If nothing much works, as I suspect it may not (from your description) - I suspect your Juke may have a Can-Bus system, which probably needs a proper Can-Bus interface unit to be fitted. You cannot just tack a tow socket onto it without..
 
Last edited:
Car have been canbus for decades. Just needs a relay like a TEB7AS if not using manufacturers loom. OP hasn't said who fitted the electrics? Assuming there is a relay it may be worth checking what it's powered from - hopefully not that chunky 12S feed that's only live with the engine running or a bit of unpowered canbus wiring or even a non permanent live like a 12v accessory socket in the boot*

* Reminds me, I must sort out my own temporary install, every summer I plug the caravan in to find nothing works till I remember and turn the ignition on!
 
cdbe said:
Car have been canbus for decades. Just needs a relay like a TEB7AS if not using manufacturers loom. OP hasn't said who fitted the electrics? Assuming there is a relay it may be worth checking what it's powered from - hopefully not that chunky 12S feed that's only live with the engine running or a bit of unpowered canbus wiring or even a non permanent live like a 12v accessory socket in the boot*

* Reminds me, I must sort out my own temporary install, every summer I plug the caravan in to find nothing works till I remember and turn the ignition on!
Click to expand...
Nothing wrong with canbus, never suggested there was. But the systems need leaving alone, connecting other wires to existing system wires is a recipe for disaster (this system in question sounds likely).

Dedicated connectors are easily available, and designed for such things as towbar.

Sounds like a non professional fitting
 
cdbe said:
Car have been canbus for decades. Just needs a relay like a TEB7AS if not using manufacturers loom. OP hasn't said who fitted the electrics? Assuming there is a relay it may be worth checking what it's powered from - hopefully not that chunky 12S feed that's only live with the engine running or a bit of unpowered canbus wiring or even a non permanent live like a 12v accessory socket in the boot*
Click to expand...

Adding 2 + 2 and making 5....

I suspect the 'MOT test instrument', perhaps drew no current/maybe used LED's, a small amount of current which the Can-Bus was able to source.

Where many installers get it so badly wrong, is in that they fail to take account of volts drop in a 12v system with relatively long cable runs. They use cable suitable for the current, ignoring volts drop...

I have a proper Can-Bus interface fitted, which requires an independent always on supply. What I did was run a 4mm doubled up (2x4mm), from a ready fused supply for the purpose, close to the battery, all the way to the rear. That fed the voltage sensing fridge/battery charge 12S, and the Can-Bus adaptor. The proper Can-Bus unit, included checking the trailer lights were working as the should, and flagging up any faults on the dash matrix, disabling the reverse sensors and car fog lights, when a trailer is connected.
 
Perhaps worth mentioning that a "dedicated" interface (i.e. one that works with the vehicle's CAN system, rather than just stops the warning lights), does a great deal more than just work the trailer lights. Most importantly, (depending on the age and complexity of the towing vehicle), it changes the Electronic Stability Control programme to give you really clever anti-snake, using the sensors already in the car, and the actuators on each brake. It also tends to kill the parking sensors on the car, so you don't have them going off all the time you're reversing with the trailer connected. it usually turns off the blind spot detection system (so it doesn't keep picking up the trailer), it kills off the rear foglight(s) on the car, so you still get the one on the trailer, but you don't keep getting dazzled in the mirror by the reflection of your own one on the car. Depending on the complexity of the car, it can also do other things too - like making the 4WD cut in earlier when setting off.
 
Harry Bloomfield said:
Adding 2 + 2 and making 5....

I suspect the 'MOT test instrument', perhaps drew no current/maybe used LED's, a small amount of current which the Can-Bus was able to source.

Where many installers get it so badly wrong, is in that they fail to take account of volts drop in a 12v system with relatively long cable runs. They use cable suitable for the current, ignoring volts drop...

I have a proper Can-Bus interface fitted, which requires an independent always on supply. What I did was run a 4mm doubled up (2x4mm), from a ready fused supply for the purpose, close to the battery, all the way to the rear. That fed the voltage sensing fridge/battery charge 12S, and the Can-Bus adaptor. The proper Can-Bus unit, included checking the trailer lights were working as the should, and flagging up any faults on the dash matrix, disabling the reverse sensors and car fog lights, when a trailer is connected.
Click to expand...

Sorry, I didn't see your last bit! Again, on some cars, I think if it detects a caravan battery plugged in, it can revise the alternator output to make it charge the leisure batteries in the caravan at a higher priority than the car's battery if needed.
 
Know anyone with a trailer board that you can borrow to prove the MOT tester at this garage (drawing low current) works but the trailer board doesn't? Or buy one at around £25 to £30? Screwfix and Halfords sell em

Towbars should be fitted by Towbar fitter specialists who understand caravan and modern car electrics. But they are rarer than hens teeth. The ones at Broadland Towbars in Norwich were good when I had a bar fitted when I lived in Lowestoft, Suffolk, to a Ford Galaxy.
 
Avocet said:
Perhaps worth mentioning that a "dedicated" interface (i.e. one that works with the vehicle's CAN system, rather than just stops the warning lights), does a great deal more than just work the trailer lights. Most importantly, (depending on the age and complexity of the towing vehicle), it changes the Electronic Stability Control programme to give you really clever anti-snake, using the sensors already in the car, and the actuators on each brake. It also tends to kill the parking sensors on the car, so you don't have them going off all the time you're reversing with the trailer connected. it usually turns off the blind spot detection system (so it doesn't keep picking up the trailer), it kills off the rear foglight(s) on the car, so you still get the one on the trailer, but you don't keep getting dazzled in the mirror by the reflection of your own one on the car. Depending on the complexity of the car, it can also do other things too - like making the 4WD cut in earlier when setting off.
Click to expand...
And people insist on tampering with canbus wires
 
I fitted a towbar to a car with canbus and it was easy as long as the instructions were followed. Quite obviously the OP's tow bar has been fitted by a bunch of ****ing monkeys. Tow bar fitting isn't cheap take it back and tell them to do it properly.
 
Fred Blogs said:
I fitted a towbar to a car with canbus and it was easy as long as the instructions were followed. Quite obviously the OP's tow bar has been fitted by a bunch of ****ing monkeys. Tow bar fitting isn't cheap take it back and tell them to do it properly.
Click to expand...

I have always fitted my own, including the mechanical and the electrics, so I know it is done, and done properly. Many of the installers use scotch lock, insulation piercing connectors, t. o splice into the existing wiring. Trouble is, the slightest bit of moisture and the connector and wiring is rotted away to nothing. A proper, reliable job needs all connection to be soldered, and heat shrink sleeved.
 
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