I'm planning to fit a towbar and 7-pin electrics to my July 2005-built 9N3.

I'm expecting to have to add 1 to the cluster coding, which should enable the trailer turn warning light. Apparently that looks like this <1> and comes on whenever you indicate whilst towing, and fails to come on if an indicator bulb on trailer or car is out.

 

Studying the factory wiring (which is for 13-pin electrics but both my trailers have 7-pin, so not doing that), I can't see how 'the car' knows whether or not a trailer is present/plugged in? I'm looking at "Trailer operation, from May 2005" and  was a bit surprised to see that all the bulb feeds barring foglight  just tap directly into the existing wiring, nothing fancy. Foglight on car switched out by 'F216' switch in socket seems like the best candidate but it doesn't seem to do anything except open-circuit the foglight bulb on the car (which will simultaneously be replaced by the one on the trailer as the plug is inserted.

 

So how does the car know when/whether you've got a trailer lighting board connected?

What am I missing?

 

Cheers for any ideas 🙂

 

I would of expected an interface box between the lights and the trailer socket, I can only think the extra load of the trailer indicator bulb is sufficient for it to know the trailer is connected and put on the extra warning light in the speedo ??

Ah yes, that would do it, I guess. Cheers.

 

Yeah I thought it was more complicated than it is.  On my 9N I put one of those bypass relay things in (before I even thought of looking up the factory wiring), seems I needn't have bothered.

I fitted a bypass unit when I wired up my 03 Octavia, but that was mainly due to the car having a bulb failure system and some people had problems (false warnings) by connecting direct to the bulbs, but was cured with the bypass unit

 

Not sure about the extra loading if the trailer has LED lights though ?? if it does you might need to add ballast resistors on the trailer  

The trailer that I barely ever use has LEDs, the one I use all the time has proper bulbs, so should be OK. 🙂 

Will let you guys know how it goes once I've fitted it all.

We did dad's Fabia (pretty much the same thing as a 9n) with a generic bypass relay and it's been fine. No dashboard indicator, but you get a buzzing from the relay when you indicate. 

 

 

On the Octy, you had to replace the hazzard switch for a different dash number to get the warning on the dash when the trailer was connected, but it was a bit hit n miss if it gave a warning so I also fitted an audible buzzer in the boot just to be 100% legal 

 

We did dad's Fabia (pretty much the same thing as a 9n) with a generic bypass relay and it's been fine. No dashboard indicator, but you get a buzzing from the relay when you indicate. 

 

 

 

Yeah that's what I did with my 9N, thinking it was necessary, but it turns out you don't need it if you can recode the central electrics module (not intstrument cluster as I mentioned earlier in error). Registered VCDS Lite will do the recoding job.

The buzzing of the bypass module was not really loud enough to hear over music, and with an LED light-board it was an almost inaudible cheep.

 

Doing it like the factory wiring saves having to put a power feed in for the bypass module, and in turn saves the added parasitic drain from that bypass relay if it's connected to a permanent supply (as they recommend, ISTR).  I added a switch in the power circuit to disconnect it when not towing but it was a pain to remember.

 

Ripped the bypass thing out at lunchtime, wired everything in direct, recoded the Central Electrics (09) module to 1 more than the old coding and it just works! 😁

 

As Nige correctly predicted, it doesn't register with LED indicators - as fitted to one of my trailer boards - but that should be easy to overcome by just shunting the LEDs with some suitable low-resistance, highish power resistors to ground.  

 

I'll take some photos of how to wire it into the existing wiring when I do the 9N3; hopefully it'll be towbarred-up at the weekend with 'almost' factory wiring.  

 

 

@Pete1 did you go with the 13 pin or just the 7N connector ? as the 13 pin makes it an MOT testable item, not that it was ever tested on my old Octy, and my Treg is due for test before the end of the month and even though it came from the factory with the swivelling towbar and 13 pin connector built into the arm, it doesn't strictly conform to the 13 pin wiring requirements as the (15) supply and the ground for the "Fridge" supply is missing, not looking forward to ripping the interior out to run the extra supply line in.

I went 7-pin for the MOT reason as well as the simple fact that both of my existing trailers use 7-pin and I don't envisage adding to my fleet of towables.   

I would've thought that if the signalling lamps work correctly on the test device for 13-pin, it'll pass.  Can't see why the power feeds to trailer have any impact on vehicle safety so as such wouldn't expect them to be checked by the test device?

Edited 8 October, 20205 yr by Pete1

Not until we get into active safety systems on trailers, but I think that's a long way off ever becoming widespread. 

 

Not until we get into active safety systems on trailers, but I think that's a long way off ever becoming widespread. 

 

Already fitted to a lot of caravans https://www.alko-tech.com/uk/al-ko-trailer-control-atc it needs the supply from the car 

Interesting; a world I know/knew nothing of.

🙂

 

I discovered at lunchtime that a 22Ω resistor to ground from each indicator connection of the LED trailer board is enough to fool the Central Electrics that there is a trailer connected, but only with engine running.  Ignition on only (lower voltage) it was hit and miss whether I got the dash indication, so I've gone for half that (2x 22R in parallel) across each LED indicator to be sure.  Had a bunch of 10W ceramic resistors kicking about from a historic project, so nice to repurpose them.