13 Pin Socket – Basic Fault Finding
The 13 pin plug on the trailer has a link between Pin 12 and Pin 3 (road light earth) so when you plug-in the trailer or caravan, it 'shorts' pin 12 on the towing vehicles socket to earth and the vehicle's ECU detects this and activates any Trailer Stability Program on the vehicle. The full ISO standard is ISO 1446 for 13 pin connections.
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