RV Outlet Installation: Upgrade Your Camper!

Hello,

I bought an A6 Allroad, model year 2009, with a factory-installed tow hitch. Unfortunately, pins 9, 10, 11, and 13 are not connected in the socket, and I need to add them to provide power for the caravan. As far as I know, you can buy these contacts individually, so it shouldn't be a problem.
Since the battery is located at the rear, the effort involved should be relatively minimal.
However, I need a constant power supply (terminal 15) for the refrigerator.
Is there a terminal marked "15" somewhere on the back?
I would then use it as a control line for a relay.
Unfortunately, I don't have a schematic diagram, which is why I'm asking this question.

Best regards, Benno.

Hi there,
In an original AHK (trailer hitch), contacts 9 (permanent power) and 13 (ground) should normally be present. These are already installed on my vehicle, which was manufactured in that year.
If you need to upgrade the wiring, you will need a 2.5 mm² connection and a 30A fuse for the constant positive connection (12V). Connect the constant positive wire to the central electrical system, and connect the ground wire to a grounding point in the trunk. It is possible that the entire wiring harness up to an intermediate connector is already present, meaning the tow hitch might have been retrofitted after all.
If I understand correctly, you want to use a relay connected to terminal 15 to only pass the constant positive voltage when the ignition is on. I would place the relay under the dashboard, as there are even slots for additional relays and fuses there, and terminal 15 can also be found there.
hg
Herbert.

PS - Is it possible to purchase a complete wiring harness from the parts department for retrofitting the tow hitch?

Herbert wrote:

(...) You will need a 2.5 mm² connection and a 30 A fuse for the 12 V constant positive terminal in each case.

"Typically, 2.5mm² wire is only fused up to 25A. However, the trailer socket is rated for a maximum of 20A, so I wouldn't fuse it higher than that. (The caravan usually only draws around 10A per circuit anyway)."

Herbert wrote:

You take the continuous positive connection from the main electrical panel.

Why this recommendation, Herbert?
If I saw a second battery in the trunk, I would be more inclined to use that one to power the campervan. That way, even if you watch TV or something for too long in the campervan, the car will still be able to start.
Newer cars usually prevent the engine from stalling, but it's still not ideal to be without power in the camper van. Therefore, it's better to use the rear battery for that purpose. That's exactly what I did with my 3C.
Do modern vehicles with start-stop systems and voltage boost technology actually finally take into account the state of charge of the second battery? Until now, I was only aware that this applied to the front battery.


On at least the Passat 3C, there is a switched positive terminal on the trailer hitch control module (THCM) located in the rear, on the left side. This could be used with a relay to provide switched positive voltage for pin 10 via a secondary battery.

Greetings.
Sure.

Here is the translation of the text from German to English:

"Guste" means "gust" in English. It refers to a sudden and strong gust of wind.

guste100 wrote:

If I see a second battery in the trunk...

The A6 4F doesn't have a second battery in the trunk, but rather no battery in the engine compartment. Therefore, even the main battery in the trunk is also a 110AH one.

Quote:

2.5mm² is typically only fused up to 25A. However, the trailer socket

is only approved for use up to 20A, so I wouldn't fuse it for a higher current.}
For me, the factory setting is 30A. The 20A limit is quickly reached with a refrigerator running, plus some lights and television.
hg
Herbert.

Oh, I overlooked the fact that the rear battery is the main battery. Then, please remove the sentence from me .

Herbert wrote:

Mine are factory-set to 30A.

Wow. That surprises me! I'm not aware of any AHK (trailer hitch) socket or 13-pin connector that is rated for more than 20 amps (I looked into this when I was retrofitting mine).

Herbert wrote:

The 20A can be reached quickly with a refrigerator and some lighting and television.

The refrigerator is typically powered through pin 10/11 to prevent it from draining the battery when the vehicle is stationary. The lights and TV, on the other hand, are powered through pins 9/13.

Furthermore: I don't know anyone who runs the TV and refrigerator at the same time . The refrigerator is normally only used during travel and turned off when stationary to conserve the battery. Using the TV while traveling makes little sense, or is only for the very brave and motion-sick resistant among us .

I'm familiar with refrigerators up to 125W (150L Dometic, pin 10/11).
"In the campervan segment, battery chargers typically have an output of 8A and therefore consume approximately 10-12A. They are usually connected via a charging plus terminal and draw the main power supply through a permanent positive connection (9/13). More powerful battery chargers don't make much sense in campervans because the voltage drop at the input becomes too large."
While it's technically possible to use appliances directly without a charging booster (excluding refrigerators) with currents exceeding 20A in modern campervans, it's generally not common for extended periods (and even at 25A, a 20A fuse will still hold for several minutes).

Furthermore, calculate the voltage drop with a 20A current using 7 meters of positive cable and 7 meters of negative cable, both with a cross-section of 2.5mm², and see what voltage actually arrives at the distribution box in the caravan. You'll already be missing 2 volts. By the way, 2x7 meters is quite short. In most cars, you typically have 3-4 meters of positive cable and about 1 meter of negative cable. In a caravan, it's usually around 2x5-8 meters if the distribution box is located relatively centrally. In the worst case, you could be missing as much as 3 volts.

PS: Out of curiosity: Which vehicle comes with 30A from the factory? Is only the trailer hitch connected to pin 9 on the fuse box, or are there other consumers connected as well? Is there anything noticeable about the socket that might indicate it can handle more current? This might be interesting for a camping forum.

Greetings.
Sure.

Here is the translation of the text from German to English:

"Guste" means "gust" in English. It refers to a sudden and strong gust of wind.

The discussion only makes sense if we're talking about a temporary 12V power supply while the vehicle is stationary. For longer periods of inactivity, it's logical to use 220V (if available) or gas for the refrigerator. Otherwise, you are right.
Vehicle: See signature for details. The manufacturer of the original tow hitch is Westfalia.
Best regards.
Herbert.

After checking again, I realized that pin 9 is already in use. I only need a constant power supply when my solar panel system isn't producing enough energy due to lack of sunlight. In the caravan, I have a battery that is normally charged by the solar panel system. However, on cloudy days, this isn't sufficient. That's why I also installed a charger as a backup, which is only used in emergencies to charge the battery while driving.
Ignition plus is only for the cooler.
Since the battery is located at the rear of this vehicle, retrofitting is quite simple. Only a control wire for the relay is needed.
There's a trailer control unit in the right rear fender well; could there be terminal 15 located somewhere there?

Best regards, Benno.

Benno wrote:

Isn't the trailer control unit located in the right rear fender well?

Could there possibly be terminal 15 somewhere there?
12-pin connector, pin 2 is terminal 15. Cable color: black.

Then use a relay to control this, and with the relay, pass voltage from the battery to pin 10. Don't forget the fuse near the battery.
Don't forget to connect pin 11 as ground }.

Just so you know: The "Dauerplus" terminal on your device is protected with a 15A fuse.

Greetings.
Sure.

Here is the translation of the text from German to English:

"Guste" means "gust" in English. It refers to a sudden and strong gust of wind.

You're welcome, Guste100!

That's exactly what I wanted to know.

Benno.