9.2 Truck-and-trailer Connections and Final Checks
Key Takeaways
For a drawbar trailer, inspect the coupling assembly, guide flange, towing and locking pins, eye and connections using the manufacturer’s procedure.
After slow engagement, perform the specified tug and direct visual checks, then connect and test the functional systems.
Before uncoupling, secure the trailer and lower its support if fitted, disconnect and stow lines, then release the towing connection.
Recognise the different coupling
A rigid truck towing a trailer may use a drawbar eye and towing pin or another approved coupling, rather than the kingpin and fifth wheel of a semi-trailer. A dog trailer has axle groups toward the front and rear; a pig trailer has its group nearer the centre. Their steering, support and load-transfer behaviour differ. Identify the actual configuration and use its procedure.
The coupling must be suitable for the trailer and rated loads, securely mounted and in sound condition. Inspect the guide flange, towing and locking pins, drawbar eye, release device, mountings and any required secondary security. Damage, excessive wear or an incompatible eye is not fixed by a strong tug. Manufacturer wear limits and ratings govern the actual component.
Prepare the trailer
Park on firm, level ground and align truck and trailer straight. Ensure the surface can support a drawbar support leg if fitted. Apply the appropriate brakes and chock as required so the trailer cannot move unexpectedly. Keep people away from the drawbar and coupling crush zone. Never use a helper’s hands to hold an eye in place while the truck reverses.
The handbook explicitly notes that procedures can vary with configuration and manufacturer recommendations. Some couplings engage automatically; others need additional pin or latch actions. Know how the lock indicates correct engagement and how the secondary device is secured. Do not assume a released lever means the same thing on every coupling.
Coupling sequence
| Stage | General handbook task | Safety purpose |
|---|---|---|
| External check | Inspect coupling and set it for coupling | Confirm suitability and readiness |
| Secure trailer | Use brakes or chocks as appropriate | Prevent unexpected trailer movement |
| Initial reverse | Move close without touching the drawbar | Allow height and line checks |
| Alignment | Adjust eye height and alignment safely | Avoid striking or false engagement |
| Engagement | Reverse slowly until correctly connected | Establish mechanical connection |
| Verification | Tug test and direct visual check | Confirm secure locking |
| Connections | Connect air and electrical systems | Restore braking and lighting functions |
| Travel setup | Raise/stow support and complete checks | Ensure clearance and readiness |
After engagement, gently perform the specified tug test, then look at the actual towing connection. Confirm the pin, latch and any secondary lock are in their correct secured positions. Do not rely only on an audible click. If the result is uncertain, stop and repeat or repair through the proper procedure.
Air lines and electrical leads
A trailer supply/emergency line supplies air to the trailer system. A service/control line communicates the brake application. Identify the actual markings and connections; colour conventions help but are not a reason to connect without checking. Inspect seals, couplers and hoses for dirt, cracks, damage and leaks. Crossed or incomplete connections can impair braking.
Electrical connections supply required lights and, where fitted, braking electronics. An ABS or Electronic Braking System cable can be separate from the ordinary lighting lead. Connect the required cables correctly, secure any locking rings and check the warning indications. Do not assume that working tail lamps prove electronic braking power is connected.
Route lines with enough slack for normal articulation and suspension movement, while keeping them away from tyres, the tail shaft, sharp edges and dragging on the road. Too little slack can tear a line during a turn; excessive unsecured slack can catch moving parts. Inspect the full travel configuration rather than only the straight parked position.
Final functional checks
Check air pressure and listen for leaks with the vehicle secured under the procedure. Confirm service and parking functions and the required trailer-protection checks. Check every trailer light, marker and indicator. Raise and stow the drawbar support leg if fitted and confirm it cannot strike the road. Remove and stow chocks only after the vehicle is secured and ready to move.
At the first suitable controlled movement, verify the vehicle behaves normally using the operator’s procedure. An unusual pull, warning or noise requires stopping and assessment. Do not treat the first highway descent as a test of a newly connected trailer.
Uncoupling a truck and trailer
The handbook’s general sequence starts with firm level ground, straight alignment and applied parking/protection controls. Secure the trailer by the stated tug or chock method. Lower the drawbar support leg if fitted so separation will not allow the drawbar to fall. Disconnect and secure the hoses and cables, then release the towing connection and move the truck slowly forward. Watch the mirrors to confirm separation.
A support leg is not a brake. Trailer brakes or chocks must still prevent movement, and the ground must support the leg. Stow disconnected couplers on suitable holders to keep out water and dirt and prevent snagging. Do not leave lines hanging where the truck’s moving components can catch them.
If the pin is under load or refuses to release, use the manufacturer’s safe method rather than hammering or placing someone between vehicles during movement. Reassess ground, alignment and load. Equipment that will not secure or release correctly needs repair.
Key decisions
Use the drawbar procedure for a drawbar trailer, verify mechanical locking directly and test every functional connection. Support and trailer security must be established before releasing the towing connection.
Official sources
Official handbook, truck-and-trailer coupling and uncoupling, pages 69–70; manufacturer instructions for the actual towing coupling and connections. Sources checked 10 October 2026.
Before releasing a drawbar coupling during uncoupling, what must be established?
Only that the truck engine is idling
That the trailer is free to roll away
That the lighting cable is left stretched across the gap
Trailer security and suitable drawbar support if fitted, with lines disconnected and stowed through the correct procedure
Sections you finish are checked off in the contents.