Final answer:
It is a good idea to lock the glad hands together or to a dummy coupler when not pulling a trailer for several reasons: it prevents air from escaping, serves as a secondary air tank, and keeps dirt and water out of the brake lines.
Step-by-step explanation:
When not pulling a trailer, it is a good idea to lock the glad hands together or to a dummy coupler for several reasons. First, it keeps air from escaping, which helps to maintain the pressure in the brake system. This is important because if the air escapes, the brakes may not function properly.
Second, locking the glad hands together or to a dummy coupler can turn the brake circuit into a secondary air tank. This can be useful if there is a sudden loss of air pressure in the primary tank.
Lastly, locking the glad hands or using a dummy coupler can help keep dirt and water out of the brake lines. This is important because dirt and water can cause damage to the brake system and affect its performance.