Quick recognition
Tow bar that does not click into the locked position
Roadmaster, Blue Ox, and Demco tow bars all use a positive-engagement latch that clicks audibly when the pivot is fully seated. Anything less than a clean click is incomplete engagement and will let go.
Safety pin missing from a tow-bar pivot
Each pivot has a primary latch and a secondary safety pin. The safety pin is removable for maintenance and is the most commonly forgotten step in the morning hitch-up.
Dinghy steering wheel that resists turning while parked
A dinghy in tow needs the steering unlocked so the front wheels can track the motorhome's path. A locked steering column on departure means jerky steering during tow and accelerated wear on the tow-bar pivots.
Dinghy transmission in the wrong mode for flat-tow
Each year, vehicle manufacturers publish a list of flat-towable models with specific transmission positions (neutral with key in accessory, transfer case in neutral, etc.). Family Motor Coach Association publishes the consolidated annual list. The wrong mode destroys the transmission within miles.
Brake-pedal pulsation in the dinghy steering wheel sensed from the motorhome
The supplemental brake system inside the dinghy activates from the motorhome's brake pedal. A faulty install or low compressed-air supply makes the dinghy intermittently brake itself, which transmits as a faint pulsation up through the tow bar to the motorhome driver's seat.
Tail light failure on the dinghy mid-trip
The 7-pin harness from motorhome to dinghy is the most failure-prone connection. A broken pin or chafed wire turns the dinghy invisible at night. Walk around at every fuel stop and verify dinghy brake lights and turn signals with a helper behind the rig.
Response protocol
- 1
1. Pre-departure walkaround (the 8-point check)
Pivot-1 latched. Pivot-2 latched. Safety pin 1 in. Safety pin 2 in. Safety cable 1 crossed and connected. Safety cable 2 crossed and connected. 7-pin harness connected. Supplemental brake powered and signaling. Verbalize each point as you touch it.
- 2
2. Drag test at low speed
Pull forward 20 feet, brake gently, check rear-view. The dinghy should follow without yawing. Any yaw indicates a steering-unlock issue or a tow-bar pivot that did not seat.
- 3
3. First-stop verification
Within the first hour, stop and walk around. Hand-test each connection. Tow-bar pivots are warm in normal operation; one pivot painfully hotter than the other indicates a binding bearing.
- 4
4. Every-fuel-stop walkaround
Same 8-point check every fuel stop. Vibration loosens pins; debris fouls latches; a stop is the natural inspection interval.
- 5
5. Disconnect at destination
Disconnect in reverse order: brake system, harness, cables, safety pins, pivots. Stage the tow bar so it does not drag on the pavement; many tow bars have a parking position that locks them flat.
- 6
6. Inspect the dinghy's tires after every tow day
Front tires take the cornering load during tow and wear faster than they would in normal driving. Rotate dinghy tires every 5,000 towed miles to even the wear pattern.
Prevention
Buy from one manufacturer for the whole system
Roadmaster, Blue Ox, and Demco each sell complete kits — tow bar plus base plate plus cables plus brake — engineered to work together. Mixed-brand systems work but introduce edge cases in load paths and warranty disputes.
Have the base plate installed by a certified shop
Base-plate installation is a frame modification. RV-specialty shops and dealer-rep installers have the templates and torque specs; backyard installs frequently mis-locate the plate, which loads the frame asymmetrically.
Use a supplemental brake even if state law does not require one
All but a few states require a supplemental brake above some towed weight. The states that do not require it still allow liability claims against drivers whose dinghy failed to brake in a panic stop. The system pays for itself in one near-miss.
Cross safety cables under the tow bar
SAE J684 specifies crossed cables. The cross catches a dropped tow-bar tongue before it touches pavement. An uncrossed pair lets the tongue scrape and break the cables one at a time.
Replace cables and harness every 5 years
Cables corrode internally and lose strength without visible cracking. Harness wires chafe through over years. Calendar-replace every 5 years even if no visible fault.
Verify dinghy fluid levels before every tow
Some flat-towable vehicles cycle their transmission cooler during tow and lose fluid through evaporation or seal weep. Check transmission fluid before every long tow day per the vehicle's owner's manual.
Real case studies
Family Motor Coach Association annual dinghy-towable list
FMCA publishes an annual consolidated list of factory-flat-towable vehicles, with the specific transmission and transfer-case positions each manufacturer requires for safe flat tow. The list is the authoritative cross-reference because manufacturers publish their flat-tow guidance in service literature that owners rarely read.
Lesson: Verify your dinghy is on the current-year list before purchase. Older models that were flat-towable in a previous body style sometimes lose that approval when the platform changes.
Source: Family Motor Coach Association — Dinghy towing guide
SAE J684 safety chain and coupling standard
SAE International's J684 standard defines the engineering requirements for safety chains and crossings on towed equipment, including crossing direction, attachment-point geometry, and strength rating relative to the towed weight. RV Industry Association installation guidance for tow bars references J684 directly.
Lesson: The cross-the-cables-under-the-bar rule is from J684. It catches a dropped tongue before pavement contact and prevents the runaway-dinghy scenario that defines the worst flat-tow failures.
Source: SAE International — Standards
What authorities don't always tell you
Editorial secrets
Most state laws require a supplemental brake above 1,500 lb towed
The thresholds vary — California requires brakes above 1,500 lb, most states above 3,000 lb, a few above 5,000 lb. A current passenger sedan dinghy is well above 3,000 lb. Drive across state lines, drive into the stricter state's rules.
Tow-bar pivots wear from misalignment, not just from miles
If the motorhome receiver and the dinghy base plate are at meaningfully different heights, the tow-bar pivots load asymmetrically. The pivot that takes the higher load wears faster and develops play. Adjust the receiver height or shim the base plate to match.
Some flat-towable models require periodic transmission cycling on long trips
Jeep Wrangler, Ford F-150 with the right transfer case, and several others ask for a transfer-case re-cycle every few hundred miles. Read the owner's manual for the dinghy's annual flat-tow chapter.
Supplemental brake batteries die in storage
Air-activated systems (Roadmaster InvisiBrake, Demco Stay-IN-Play) draw key-off current from the dinghy battery. After 6 weeks of storage the dinghy battery is dead and the brake will not arm. Hook a trickle charger to the dinghy during storage.
Backup-light wiring on the 7-pin harness is for the motorhome, not the dinghy
The pin numbered for reverse signals in the 7-pin convention sends current from the motorhome to the dinghy. On most flat-tow setups the dinghy reverse lights are not wired, which means the dinghy is invisible while backing the motorhome. Avoid backing the rig while towed — disconnect first.
Equipment recommendations
Generic categories — no brand endorsements. Verify current specifications against the manufacturer's documentation.
Tow bar, motorized or manual extension
Spec: Roadmaster Falcon All-Terrain, Blue Ox Avail, or Demco Commander; rated to the dinghy's GVWR with a 50 percent margin.
Storage: Stows in the motorhome's rear receiver between trips.
Vehicle-specific base plate
Spec: Brand-and-model matched to the dinghy; installed per shop torque spec.
Storage: Permanent install in the dinghy's frame.
Safety cables, rated to dinghy GVWR
Spec: SAE J684-compliant, crossed under the tow bar.
Storage: Attached to the tow bar between uses.
Supplemental brake system, in-vehicle
Spec: Roadmaster InvisiBrake, Demco Stay-IN-Play, Air Force One, or M&G Tow Brake; installed inside the dinghy and signaled from the motorhome brake pedal.
Storage: Permanent install in the dinghy.
7-pin trailer harness with diode protection
Spec: Provides motorhome-to-dinghy tail-light, turn-signal, and brake-light signaling without back-feeding the dinghy's own brake-light circuit.
Storage: Permanent install in both vehicles; connect for each tow.
When to call 911 vs ER vs self-care
Call 911 now
- Dinghy fully separated from motorhome and loose on roadway
- Tow-related collision involving other vehicles
- Injury during emergency disconnect
Drive to ER
- Hand or finger injuries from cable failure (frayed steel cable cuts deep)
- Back strain from emergency dinghy disconnect
Urgent care
- Lacerations from broken safety chain links during inspection
Self-care at home
- Dinghy disconnect with cables and brakes intact, no injury or damage
Frequently asked questions
Can I flat-tow any car behind my motorhome?
No. Only vehicles the manufacturer specifically lists as flat-towable, with the transmission and transfer case in the published positions. FMCA's annual dinghy guide is the consolidated reference. Towing a non-approved vehicle destroys the transmission within miles.
Do I really need a supplemental brake in the dinghy?
Yes in 39 states for vehicles above the state's towed-weight threshold (typically 1,500 to 3,000 lb), and yes for liability protection in all states. The supplemental brake activates from the motorhome's brake pedal and slows the dinghy in concert with the motorhome.
What is the difference between a tow bar, a tow dolly, and a trailer?
Tow bar: all four dinghy wheels on the road, dinghy in neutral. Tow dolly: front two dinghy wheels on the dolly, rear two on the road. Trailer: all four dinghy wheels on the trailer. Each has different speed limits, state-law requirements, and dinghy-eligibility lists.
How fast can I safely drive while flat-towing?
Tow-bar manufacturers typically rate their products to 65 mph. Some states post lower speed limits for towed vehicles (California: 55 mph with any trailer or tow). The conservative answer is to set cruise at 60 mph or the state-posted towed-vehicle limit, whichever is lower.
Should I disconnect the dinghy in heavy weather?
In sustained crosswind above 30 mph, in a snowstorm with reduced visibility, or in any weather where you would not drive the dinghy alone, yes — find a safe pullout, disconnect, and drive the motorhome to shelter with the dinghy parked.
Is this page a service-manual or state-law replacement?
No. PickRV reference only. State towing laws change; check the current statute in every state on the route. Service-procedure questions go to the tow-bar and base-plate manufacturers and to RVIA-certified installers.
Sources
Related safety pages