What colour is the auxiliary line on a three-line braking system?
If you're driving an articulated vehicle or a trailer combination, it's vital that you understand the rules that apply to coupling and uncoupling the brake lines. If you take a practical driving test with a trailer, you'll be expected to demonstrate this during the test. The lines are colour-coded: red is the emergency line, blue is the auxiliary line and yellow is the service line. They must be connected strictly following the correct procedure.
Tap the Next HGV / LGV theory test question button to see the next HGV / LGV theory test question, or pick a few random questions from the list below to mix up your practice.