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Dinghy Towing Accessories

Originally Published in MotorHome Magazine

The research has been done, the financing aranged, the papers signed … and that new dinghy vehicle is now sitting in your driveway. You’ve shopped carefully to pick a model that’s certified by its manufacturer for flat-towing, you’ve checked the vehicle’s weight to confirm that it’s within your motorhome’s safe towing capabilities and you’ve ordered it with any requisite factory options to make it towable with all wheels rolling.

Now what?

As any seasoned motorhome owner will tell you, there are a lot of steps involved in getting a new vehicle to the point where it can be towed safely. Unfortunately, no automaker offers a plug- and-play solution that makes its products ready for safe dinghy towing right from the factory. Thus, it’s up to you (and perhaps a knowledgeable towing equipment dealer) to get the job done right.

Dinghy Wiring

One of the most important aspects of dinghy prep involves connecting the wiring between the two vehicles. Tail, brake and turn signals on the back of the dinghy are required in all 50 states and all Canadian provinces, so this isn’t a step that you can overlook. (Neither side clearance nor backup lights are required, and are rarely used.)

The most common source of dinghy wiring confusion revolves around differences in the way the turn-signal lights are wired on various cars and motorhomes. Some models are wired to supply turn- signal power to the same bulbs that are used for the brakelights (commonly referred to as a 4-wire system), while others use separate amber bulbs for the rear turn signals (a 5-wire system). Note that 4- and 5-wire systems are used on both motorhomes and cars, so any one of four solutions may be needed for any particular application. Adapters are readily available to electronically match the wiring systems of the dinghy and motorhome.

The traditional method of wiring a dinghy vehicle involves the use of steering diodes, which function as one-way gates to the flow of electricity, allowing power from either the motorhome or vehicle to be supplied to the rear bulbs. Because no electricity can flow backward through a diode, it also prevents power from the motorhome from being inadvertently introduced to any other circuits in the dinghy vehicle.Many late-model vehicles are equipped with on-board diagnostics that continuously check for proper operation of turn-signal and brakelight bulbs. Unfortunately, the introduction of aftermarket steering diodes into the vehicle’s wiring can “fool” this diagnostic function, typically causing it to give false warnings about burned-out bulbs.

For this reason, it is becoming more common to modify each of the vehicle’s tail-lamp assemblies to accept a separate bulb. This bulb is then connected directly to the motorhome, eliminating any connections to the vehicle’s existing wiring harness. This modification isn’t for the squeamish, since it usually involves drilling a large hole in the tail-lamp reflector. Fortunately, special snap-in sockets are available that make this job somewhat easier. Since the new socket takes up considerable space behind the lamp assembly, care must be taken in selecting a location for the new hole that avoids socket interference with any other objects behind it.

Note that most states allow the turn signals to be either red or amber in color, but only permit the brakelights to be red. Thus, on automobiles equipped with amber turn signals, the new socket is typically installed behind the red brake-lamp lens. In situations where modifications to the dinghy’s original wiring either aren’t desirable or practical, a set of removable towing lights often provides a workable solution. Most of these products are affixed with magnets, although some models can be equipped with suction cups or hook-and-loop fasteners (ideal for use on plastic or fiberglass surfaces). A cable is then snaked across the vehicle to the connector at the motorhome hitch receiver. In some cases, the cable is semi-permanently routed inside or underneath the vehicle, allowing the lights to be quickly removed and stowed inside the trunk. Several companies offer wireless, removable towing lights, thereby eliminating the need for this cable altogether.

Although many motorhomes come with a factory-installed 4- or 5-pin connector, there are situations where a different connector is necessary. Some unapproved dinghies equipped with an automatic transmission must also be equipped with an electric lube pump, which requires a connector pin for 12- volt DC power (and ideally, a separate connector pin for ground, in order to avoid drawing excessive current through the existing one). Also, some auxiliary braking systems require connections to the motor- home, further increasing the connector-pin count.

Ideally, the industry-standard connection scheme should be observed when installing this new connector, so that it can also be used when towing boats, ATVs, horse trailers, etc.

Unfortunately, since no industry-wide standard exists for wire color codes used in automobiles, another hurdle in dinghy wiring involves identifying the proper wires for the stop, turn and tail lamps (as well as a suitable ground connection). If you’ve had the foresight to purchase a service manual for your particular vehicle, this can sometimes be accomplished by visual inspection of the wire harness. More often than not, it involves connecting a test light to each suspected wire in order to match it with the corresponding bulb. Note that on 4-wire systems, the same wire may be “hot” when either the brake or one of the turn signals is operated.

When splicing diodes or other connections into the vehicle’s wiring harness, it is important to use top-quality connectors or splices. In order to prevent any chance of corrosion, all connections should be waterproof. Heat-shrink tubing works very well for this purpose, as does self-vulcanizing plastic tape.

Steering Wheel Locks

Motorhome owners who tow a dinghy backwards on a tow dolly may want a steering wheel lock that can position the steering wheel exactly where they want it. AW Direct offers several types at various price points. Such a device also acts as a backup to the factory steering lock.

Dinghy Braking Systems

Adequate dinghy braking is an important consideration, because builders tend to push the weight of their motorhomes right to the edge of the chassis manufacturer’s ratings – and the addition of up to several tons of extra rolling weight can be enough to put the combined vehicle pair’s braking performance into unsafe territory.

Furthermore, some chassis manufacturers specify that towed loads in excess of 1,500 pounds should have independent brakes and safety breakaway systems.

Although a diverse range of dinghy braking systems is available, all aim to perform essentially the same task: to apply the dinghy’s brakes in tandem with those on the motorhome.

One approach uses electronic signals generated in the motorhome to activate the dinghy-vehicle brakes. The motorhome components of the system measure deceleration and send a signal to a power unit connected to the dinghy-vehicle brake pedal. As the electronic signal varies with motorhome deceleration, the amount of brake-pedal pull varies in concert for variable braking.

The system includes a vacuum pump in the dinghy vehicle that maintains full power-brake performance. An actuation lever on the control unit in the motorhome allows the motorhome driver to apply brakes manually, if desired.

Other products include those that utilize a self-contained power pack that temporarily attaches to the dinghy’s brake pedal. This package usually contains an air compressor, air cylinder and control circuitry. Most models have a built-in inertia sensor in the dinghy that automatically applies the brakes without any direct signals from the motorhome; in some cases, a radio link or control wire is used to receive braking signals from the motorhome.

Other systems use a removable air cylinder to push the pedal, with motive power for the cylinder usually supplied by the motorhome’s existing air compressor (if air brakes are present) or an add-on electric compressor. A signal from the motorhome’s brakelights is often used to control operation of the cylinder, although inertia-sensing control boxes are sometimes used instead. One variation of this scheme uses an electric linear actuator in lieu of an air cylinder, thereby dispensing with the need for a com- pressed air supply.

Finally, a few systems use the movement in a special hitch drawbar as the motive power to operate the dinghy brakes. As the motorhome decelerates, the dinghy forces the drawbar to move forward, and the dinghy’s inertia is used to operate a flexible cable connected to the brake pedal or to move a master brake cylinder that pressurizes the dinghy’s brake lines. Self-contained systems – like those from Blue Ox, Brake- Buddy and Roadmaster – generally have a significant edge in ease of installation. The use of a supplemental braking system represents a wise investment in ultimate dinghy towing safety.

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