How can you tell if you have cross-connected the supply line and the service (control) line on a tractor-trailer with air brakes?
- (a) The trailer parking brakes will not release.
- (b) The trailer service brakes will not function.
- (c) The trailer braking system will start to leak air.
- Both (a) and (b) will happen. ✓
Answer: D. Both (a) and (b) will happen.
You have cross-connected the supply and service lines if the trailer spring parking brakes won't release and the trailer service brakes won't work.
Why this is the answer
The handbook's driving tip lists two signs of reversed supply and service line connections: the spring parking brakes won't release even when you use the dashboard parking brake control, and the trailer service brakes won't function. Since the tip gives both signs together, the correct answer is the one saying both happen. The passages do not say a cross-connection makes the braking system start leaking air; they mention air loss when lines separate or rupture.
Why the other answers are wrong
- A. (a) The trailer parking brakes will not release. — The parking brakes not releasing is only one of the two signs the handbook lists, so choosing it alone leaves out that the trailer service brakes also won't work.
- B. (b) The trailer service brakes will not function. — The trailer service brakes not working is only one of the two signs the handbook lists, so choosing it alone leaves out that the spring parking brakes also won't release.
- C. (c) The trailer braking system will start to leak air. — A cross-connection is not described as causing the trailer braking system to start leaking air; the passages mention air loss when a line breaks or separates.
Remember it
Colour-check the glad hands before you pull away: red is supply, blue is service.