It's been annoying me since I bought my car with the 3AC towbar that it doesn't have pins 10, 11 and 12 wired up in the 13 pin trailer socket. These are the ignition switched supply for the caravan fridge and its corresponding return. This means warm beer in your caravan fridge, not good.
I wanted to retro fit the missing pins and while I'm at it, include a waterproof permanent method of charging the car battery using pin 12 of the trailer socket so it is independent of any towbar wiring/modules etc.
This install is using the Ctek MXS 5.0 charger and its accessories.
Remove all the trim in the offside rear wing.
Remove the expanding rivet and remove the offside plastic storage bin.
Using the template that came with the Ctek comfort panel indicator cut out a hole for it in the storage bin.
Now to get the wires from the towbar to the Ctek comfort panel indicator.
Swivel out the towbar and clip the three tangs and remove the rear outer plastic cover on the 13 pin trailer socket, pull out the rubber grommet and roll up the bottom of this grommet over the existing wiring loom. Unclip three more tangs and using a pair of long nose pliers pull out the rear of the 13 pin trailer socket
In the three missing locations there is three clear plastic bungs, push these out.
These are the three connectors required (joined together in pic above) these have barbs on them which push into and click into place on the rear of the 13 pin trailer socket. The connector on the left in the pic above is what is bonded into the front part of the 13 pin trailer socket and is what the trailer plug, plugs into.
Solder on BMW part number 61131376204 (Size 1,0-2.5 mm^2) to lengths of 2.5mm^2 cable.
Using a bit of soap I pushed the wires thru the trailer socket grommet
Push the pins into the socket. Grey for pin 10, black for pin 11 and red for pin 12, the charging wire.
I then threaded on a length of heat shrink and a pvc sheath recovered from redundant Westfalia towbar wiring to give the three wires some protection.
Using the heat shrink, I sealed the end of the pvc sheath to the wires and the other end is covered by the sockets rubber grommet when rolled back down.
To get the wires into the boot I drilled a hole in the read bulkhead adjacent to the location where the existing towbar wiring loom passes thru it, (I painted the exposed edges of the hole as its steel) and placed a sleeved grommet into the hole.
Attach your new loom to the existing loom with cable ties and tuck it up and secure to the loom above the towbar up in behind the bumper. Thread the new cables over the top of the towbar where it bolts to the car.
Thread wires thru the grommet into the boot. Install the plastic storage bin and fit the Ctek comfort panel indicator and thread its wiring towards the battery via the existing wiring route.
Terminate the black wire from pin 11 on a ring (soldered) and connect to the convenient stud just above where I drilled the hole for the grommet. That's the earth for pin 10 sorted. Taking the red wire from pin 12 on the towbar installed and a length of black wire, solder these onto a Ctek plug, (Ctek Female connector adapter 56-689, from Halfords £5.99). This will plug into the Ctek comfort panel indicator mounted in the storage bin. The other end of this black wire is to be terminated on another ring (soldered) and fitted to the same stud.
This now provides an earth from the Ctek comfort panel indicator, it will only be earthed when the plug is plugged in to prevent the panel indicator needlessly flashing away draining the battery. I taped together the black and red wires on the loom to the Ctek plug. These are then thread up thru the fuse box access flap so they can be hidden away when not required and pulled out to charge the battery. In the picture below these are lying in the storage bin. The grey wire will go on to a smart relay to provide ignition on supply to pin 10.
Connect the positive end of the Ctek comfort panel indicator to the battery. I taped up the negative ring connection as its not required. The connection to the negative terminal for the charging circuit is made via the stud on the boot, once the Ctek plug is plugged in to the Ctek comfort panel indicator. This way the battery sensor is in the circuit when the car is charging. Do not connect directly to the negative terminal on the car battery.
Using a 13 pin trailer plug, wire a Ctek socket (one you get with the charger after cutting off the rings) to pin 12 and any one of the earths, I used pin 11. Make sure the cable entry point is sealed, I had a black grommet that fitted perfectly after enlarging the hole for the cable.
Refit all the trim.
To charge the battery. Swivel out the towbar and whilst it is in motion, plug in the Ctek plug into the Ctek Comfort panel indicator
The Ctek Comfort panel indicator will now flash the battery condition.
Plug in the 13 pin plug with the Ctek socket to your towbar. Its now fully waterproof. The Ctek plug and sockets are good for IP65 and the trailer plug and socket are at least IP44, I think.
I used a Ctek extension lead fed under my garage door to where I can safely and securely have my Ctek charger plugged in.
What I will do is lengthen the wires between the 13 pin trailer plug and the Ctek plug with some more 2.5mm^2 cable so I do not need to rely on using the Ctek extension cable, its only 1.5mm^2. All the cable/wire I used is 2.5mm^2 to limit voltage drop. All connections were soldered and protected with heat shrink.
Once I finish the wiring for pins 10 and 11 I'll include that with a bit more detail of how I installed the missing pins including the differing detail differences in the 3AC towbars fitted across the BMW range as the required pins are different on the older towbars. I have a newer towbar so I have the current 13 pin socket, not the one that was originally fitted to F10/11s.
My quest for cold beer nears its end!