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Trailer Socket


Up to now, the 13-pin outlet socket has not been able to completely replace the old 7-pin socket. Particularly as far as the comprehensive offering of rental trailersis concerned, where the sockets must be as universal as possible, will keep this trend going for still quite a while. Adapters for one or the other direction are also available ...


When adding an automatic trailer-coupling, a coplete electrical system can be installed. One then has no bother with terminal descriptions. It is of course, much cheaper to wire the outlet oneself.

Here are the terminal descriptions seen from the plug-side:

Description Function 7-pin 13-pin L
L Left indicator at the top 1
54 Brake light above left 6
54g See text! above right 2
58L Left parking light Center 7
58R Right parking light bottom left 5
31 Earth 1 - 8bottom right 3
R Right indicator bottom 4
30 Permanent plus 9
15 Plus (ignition) 10
31 Earth for 10 11
Reversing lights 8
Trailer-recocnition 12
Earth for 9 13

The wiring is fairly simple, if the lighting system is not yet controlled through the CAN-Bus, and there are no special control functions for the rear lights. One can then tap each of the two rear lights with an edge-connector. Indeed, a control-lamp for the trailer indicators is still necessary. Either an indicator relay with trailer-control (see indicator system) is already installed, or the existing one can simply be replaced. One can also use one, specially developed for trailer outlets, with an acoustic warning device. The terminal 54g is interesting because it was originally intended for the electric brake control in trucks. Nowadays, it is used for various functions, e.g., for the electricity supply for caravans, the rear fog-light- or the reversing lamp/s.

Taking a closer look, one discovers a small opener on the outlet, which is activated by the plug. This is a trailer-recognition, which switches off the vehicle fog-light during trailer operation, to avoid blinding the following traffic.


Those who uncouple the trailer first, and only afterwards pull out the plug, run the risk of forgetting the latter. Should one then drive off, the cable is mostly torn from the plug. In this case, the trailer cannot even be driven to the next workshop, because neither the brake lights nor the indicators function. The question which arises, is whether one can rewire this oneself. The following paragraphs contain a small tutorial for 7-pin plugs. Thereby, it is important, never to connect the earth-wire to the other connections, otherwise, the next time the respective function is switched on it will mean replacing a fuse. 10/06

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