Most trailer accidents are preventable. They happen because someone skipped a check that takes 30 seconds. This 10-point checklist should be run every single time you hook up a trailer — whether it's your first time towing or your hundredth. At Fondy Trailer Rentals, we do a walkthrough with every renter before they leave. This is what we check.
Print this out or screenshot it. Run through it every time you hook up — at pickup, and again after every stop where you exit the vehicle. A loose connection caught in a parking lot is far better than one discovered at 60 mph on Highway 41.
Check 1: Hitch Ball and Coupler Connection
The hitch connection is the most critical single point on any trailer setup. A coupler that isn't fully locked onto the ball will disconnect at the worst possible moment — typically during a hard brake or sharp turn.
What to check:
- Lower the coupler fully onto the ball — it should seat with an audible click or drop
- Lock the coupler latch completely — this varies by trailer type, but the latch should be fully engaged and not able to lift off the ball
- Attempt to lift the trailer tongue by hand. If it lifts off the ball, it is NOT properly connected. Start over.
- Confirm the ball size matches the coupler size. A 2-inch ball in a 2-5/16" coupler looks connected but isn't — it'll come off under load.
Check 2: Safety Chains
Safety chains are the backup if the hitch connection fails. In Wisconsin, they're required by law on all trailers. They must be crossed under the trailer tongue (forming an X) to cradle the tongue if it drops, preventing it from gouging the pavement and allowing you to maintain some control.
What to check:
- Both chains attached to the tow vehicle's hitch receiver — not to the bumper, not to plastic
- Chains crossed under the tongue in an X pattern
- Enough slack for turns but not so much they drag on the road
- Hooks fully closed and locked — S-hooks should be turned to prevent backing off; snap hooks should be snapped
Check 3: Trailer Lights
Wisconsin requires functional brake lights, tail lights, turn signals, and clearance lights on all trailers used on public roads. A trailer without working lights is an accident waiting to happen, and it's an automatic traffic stop.
What to check:
- Plug the trailer light connector fully into the tow vehicle
- Have a second person stand behind the trailer while you activate each function: turn left, turn right, brake pedal, running lights
- If you're alone, use a reflective surface or a phone camera pointed at the lights
- Check for corroded connections if any lights are intermittent or out — push the connector firmly and check for bent pins
Check 4: Tire Pressure on the Trailer
Trailer tire blowouts are serious — they can cause violent sway and loss of control. Trailer tires are often underinflated because they sit in storage between uses and lose pressure slowly. Many trailer accidents trace back to underinflated or visually deceptive tires that look fine but are actually significantly low.
What to check:
- Check pressure with a gauge — don't guess by looking
- Tire pressure is stamped on the sidewall of the trailer tire (this is the maximum pressure; run near this for trailer tires, not at the minimum)
- Check for visible cracking on sidewalls — old trailer tires crack with UV exposure even when tread looks fine; cracked sidewalls can fail suddenly
- Check that all lug nuts are tight — trailer wheels can loosen in storage
Check 5: Load Balance and Weight Distribution
An improperly loaded trailer is one of the most common causes of trailer sway and accidents. The physics are simple: too much weight behind the trailer axle creates a lever effect that lifts the rear of the tow vehicle and causes sway. Too much weight forward creates excessive tongue weight that overloads the hitch and bears down on the tow vehicle's front axle.
What to check:
- 60% of the load's weight should be in the front half of the trailer (ahead of the axle)
- Load should be centered side-to-side — no significant tilt left or right
- Tongue weight should be 10-15% of the total loaded trailer weight. If your hitch is very compressed or if the rear of your truck is noticeably squatting, you may be over tongue weight.
- For the dump trailer: do not overload. Dense materials (gravel, stone) reach weight limits before visual fullness
Check 6: Strap Tension and Load Securement
Every item on the trailer needs to be secured against movement in all directions — forward, backward, and sideways. Wisconsin law requires that loads be secured so nothing falls off during transport. An unsecured load that falls and strikes another vehicle creates both criminal liability and civil liability.
What to check:
- Ratchet straps properly tensioned — tight enough to prevent movement, not so tight as to damage load or trailer D-rings
- Ratchet mechanisms fully engaged and handles locked closed
- No straps running over sharp edges that could fray under tension
- Load can't shift forward during braking — forward movement in a crash is the most dangerous direction
- Tarps (on open trailers) secured on all four sides — a loose tarp at highway speed becomes a road hazard
Check 7: Mirrors for Trailer Width
If your trailer is wider than your tow vehicle, you legally need extended mirrors that provide a view down both sides of the trailer. This isn't just a legal requirement — it's a practical necessity for safe lane changes and backing.
What to check:
- Can you see both rear corners of the trailer in your mirrors without moving your head significantly?
- If not, add clip-on mirror extensions (available at auto parts stores) before driving
- Adjust mirrors after hitching — the trailer changes the sight line compared to driving without it
Check 8: Brake Controller Function
If your trailer has electric brakes (required in Wisconsin for trailers over 3,000 lbs when loaded), your brake controller must be functioning and properly calibrated. An uncalibrated controller either locks up the trailer brakes prematurely or applies them too late — both are dangerous.
What to check:
- Brake controller is powered on and shows the trailer is connected (most controllers show an indicator light or display when a trailer is detected)
- Apply brakes at low speed (5-10 mph in an empty lot) and feel/listen for trailer brakes engaging proportionally
- Gain setting: set appropriately for your loaded weight. Higher gain = more aggressive braking. Start at mid-range and adjust after the first few stops.
- Manual override button works — this applies trailer brakes independently, useful for testing and for controlling sway on a highway
Check 9: Spare Tire
Every towing trip should have a spare. A trailer tire blowout on Highway 41 at 6pm on a Friday is not a situation you want to resolve with a call to a tire shop. Check that a spare is mounted on the trailer (or that you have one in the tow vehicle) and that it's inflated to spec.
Check 10: Speed Limits and Wisconsin Towing Rules
This isn't a physical check, but it's essential knowledge before you drive:
- Wisconsin maximum towing speed: The posted speed limit, but recommended maximum is 55 mph for stability with a loaded trailer, especially in crosswinds
- Safety chains: Required on all trailers — crossed under the tongue
- Electric brakes: Required when loaded trailer weight exceeds 3,000 lbs
- Trailer lights: Required — all lights must function
- Securing load: Required — nothing may fall off the trailer; fines apply if material drops and damages another vehicle
- Spring weight restrictions: Posted county roads in Wisconsin reduce axle weight limits from approximately March through May. Check Fond du Lac County Highway Department postings if using county roads with heavy loads.
When in doubt, pull over and check. If something feels wrong while driving — unusual sway, a change in handling, a sound that wasn't there before — stop at the next safe location and inspect the trailer. Trust your instincts.