T7 towing hitch connector questions

[blind_oracle]

I want to abuse the towing hook connector to power some external stuff e.g. when camping.

It has (should have?) a pin 9 that is always powered, presumably from a leisure battery. I've checked, but there's no voltage there. So probably it kicks in only when the towing control unit detects that the trailer is connected.

I wonder if anyone tried to emulate the presence of the trailer? I guess I can hook the lamps, but I'd avoid that and maybe use some resistors instead?

 

[WelshGas]

I want to abuse the towing hook connector to power some external stuff e.g. when camping.

It has (should have?) a pin 9 that is always powered, presumably from a leisure battery. I've checked, but there's no voltage there. So probably it kicks in only when the towing control unit detects that the trailer is connected.

I wonder if anyone tried to emulate the presence of the trailer? I guess I can hook the lamps, but I'd avoid that and maybe use some resistors instead?

Most Towbar connections, certainly factory fit , on previous VW Californias have a microswitch in the socket that detects the plug being inserted. So maybe using a Towbar plug with just pin 9 connected?

 

[blind_oracle]

Most Towbar connections, certainly factory fit , on previous VW Californias have a microswitch in the socket that detects the plug being inserted. So maybe using a Towbar plug with just pin 9 connected?

Hmm, I've tried exactly with a towbar plug, no voltage on pin 9. Maybe I picked the wrong pin, gonna check tomorrow. Thanks!

 

[blind_oracle]

Okay, I did some testing:
1. With just the plug inserted there is no voltage anywhere
2. When I added 7 resistors 10 Ohm each (one for each lamp), the voltage on pin 9 appeared, but not on pin 10 when I enabled the ignition - for some reason. Maybe I need to check fuses
3. The resistors quickly burned out since they were very small. I need to check, maybe higher resistance works too...
4. After resistors burn out - car starts to say something like "Trailer: please check rear left light"

 

[sticky1]

Okay, I did some testing:
1. With just the plug inserted there is no voltage anywhere
2. When I added 7 resistors 10 Ohm each (one for each lamp), the voltage on pin 9 appeared, but not on pin 10 when I enabled the ignition - for some reason. Maybe I need to check fuses
3. The resistors quickly burned out since they were very small. I need to check, maybe higher resistance works too...
4. After resistors burn out - car starts to say something like "Trailer: please check rear left light"

I’m assuming you are trying to avoid using the 12v cigarette lighter socket in the rear? That runs from the leisure batteries.
I suspect the towbar electric runs from the starter battery.

 

[blind_oracle]

I’m assuming you are trying to avoid using the 12v cigarette lighter socket in the rear? That runs from the leisure batteries.
I suspect the towbar electric runs from the starter battery.

Yeah, I was thinking about getting power with the tailgate/doors closed. And 12v socket is usually bad at providing higher amperage - gets hot, melts, all that. Towbar should be able to steadily supply 15-20Amps I guess.

Indeed, the power on the towbar turned out to be from the starter battery, not that it matters much probably since the starter battery gets recharged from leisure ones if it gets too low. Though I'd prefer leisure ones directly, of course.

I've tried using only two 150 Ohm resistors, wiring them as tail lights - the trailer controller is happy and provides power, but they also get very hot (with ignition on). I'll try either using even more resistance, or putting them as turn indicators which get no power by default - maybe the controller would still be happy.

Also the power on pin 10 (marked as 'ignition' power) appears only with the engine running, ignition alone is not enough.

 

[sticky1]

Yeah, I was thinking about getting power with the tailgate/doors closed. And 12v socket is usually bad at providing higher amperage - gets hot, melts, all that. Towbar should be able to steadily supply 15-20Amps I guess.

Indeed, the power on the towbar turned out to be from the starter battery, not that it matters much probably since the starter battery gets recharged from leisure ones if it gets too low. Though I'd prefer leisure ones directly, of course.

I've tried using only two 150 Ohm resistors, wiring them as tail lights - the trailer controller is happy and provides power, but they also get very hot (with ignition on). I'll try either using even more resistance, or putting them as turn indicators which get no power by default - maybe the controller would still be happy.

Also the power on pin 10 (marked as 'ignition' power) appears only with the engine running, ignition alone is not enough.

Hopefully not 15 - 20 amps supply, you’ll blow your towing electrics fuse, if that’s cumulative usage you’ll not get many days camping.
I would consider a separate power source, such as a power bank.
You could take a feed from the leisure batteries and feed a cable through the closed rear door, I suspect the door seal would deflect enough to allow the cable to feed through.

 

[blind_oracle]

Hopefully not 15 - 20 amps supply, you’ll blow your towing electrics fuse, if that’s cumulative usage you’ll not get many days camping.
I would consider a separate power source, such as a power bank.
You could take a feed from the leisure batteries and feed a cable through the closed rear door, I suspect the door seal would deflect enough to allow the cable to feed through.

Well, there's not much official info but people on the internet are saying that "The ISO 11446 spec states that pins 9 & 10 (12V permanent power and 12V Ignition On) should provide 20A".

And half of fuses for the trailer on T7 are 25A:



(I would guess F3/F31 are for pins 9/10 and the rest is for the lamps etc, though not sure about "Trailer charging cable" which might be also 9 or 10)

So probably 15-20A would be Ok instead of running the cable from leisure batts. I am anyway, instead of a separate power bank, want to wire a bigger leisure battery in parallel with the stock ones.

Currently I've wired another 80Ah - it seems to work ok and doubles my capacity, maybe I'll increase that.