Lights, Signals, Action!

Lights,
Signals,
Action!

There are a number of good ways to modify a vehicle’s electrical system so that it can be towed behind a motorhome safely and legally

By Chris Hemer / photos by author

Lights, Signals, Action!

There are a number of good ways to modify a vehicle’s electrical system so that it can be towed behind a motorhome safely and legally

By Chris Hemer / photos by author

hen planning to tow a vehicle behind a motorhome, keep in mind that you’re essentially turning it into a trailer as far as the law is concerned. It must have an emergency breakaway, its own functioning brake system and lights that work in concert with tow vehicle (in this case, your motorhome) so that drivers behind your dinghy vehicle know when you’re braking, turning, or just have the running lights on.

Unlike a trailer, which already has a wiring harness designed to plug into the tow vehicle (seven or four pin), a car, truck or SUV does not — the electrical system in the dinghy vehicle must be modified so that can be plugged into the motorhome’s electrical system when it’s time to tow. This same harness may also be used to operate a supplemental braking system and/or to keep the dinghy vehicle’s battery charged with the addition of a charge line (more on that later).

Thankfully, dinghy towing is such a common practice today that there are ready-made kits that enable an electrical connection to the motorhome without having a degree in electrical engineering. These can be divided into three basic types: Prefabricated application-specific harnesses that plug and/or splice into the dinghy’s electrical system; universal towed-car wiring kits; and so-called “bulb and socket” systems. Obviously, a plug-and-play prefabricated harness would be the easiest way to go — if one is available for your vehicle. Companies like Blue Ox (blueox.com/recreational-commercial-flat-towing/towing-accessories/ez-light-wiring-kits/), Demco (demco-products.com/rv-towing/towed-connectors) and Hopkins Towing Solutions (hopkinstowingsolutions.com/products/vehicle-wiring-kits/) all offer fit lists that make it easy to find out. If not, a universal wiring kit can be made to fit almost any vehicle by splicing into the existing electrical system.

Roadmaster’s Economy Wiring Kit includes a 27-foot length of four-wire electrical cord; 3 feet of split wire loom; a ring terminal, cable ties and wire connector. The kit also includes four of the company’s Hy-Power diodes.

Lastly, a bulb-and-socket system bypasses the vehicle’s electrical system altogether with separate wiring, and individual bulb/socket assemblies that mount inside the existing tail lamp housings. The vehicle year, make and model, as well as who will be performing the installation (you or an RV repair center/dealer) will likely dictate which wiring solution will work the best.

As we alluded to earlier, each wiring solution will include a wiring harness that is routed from a receptacle located on the dinghy vehicle to another receptacle on the motorhome when you’re ready to tow. In some cases, wiring kits that incorporate the vehicle’s electrical system may also include one-way diodes, which prevent electrical “backflow” from the motorhome’s electrical system to the dinghy (and vice-versa), which can cause damage to both vehicle systems. Companies like Blue Ox, Demco, Hopkins Towing Solutions and Roadmaster all offer viable choices.

This schematic for the Roadmaster Economy Wiring Kit (part number 152) illustrates how a typical dinghy wiring job is performed. Because the kit is universal, however, some changes/additions may be required depending on the vehicle.

If you don’t like the idea of monkeying around with the vehicle’s electrical system, another option is auxiliary lights that attach temporarily to the vehicle with suction cups or magnets (similar to what a towing company may use if it needs to tow your vehicle to a repair center). These may be a good choice if you tow more than one vehicle and/or only dinghy tow once in a while, and don’t want to invest the extra time and money in a wired system. These kits include a power cord that is routed from the rear to the front of the dinghy vehicle and plugged into the motorhome when it’s time to tow. By and large, however, wiring the electrical system into the dinghy vehicle is still the best option if you plan to tow frequently.

As you’ve likely surmised, not all vehicle electrical systems are the same — so check your vehicle owner’s manual (most are available online if you can’t locate one) for the required towing practice. Some vehicles require that specific fuses be removed or that the negative battery cable be disconnected before towing, which is not only a hassle, but may create other problems as well. For example, if the vehicle’s electrical system is not energized, the dinghy vehicle’s supplemental braking system may not work and its power brake system will not function to its fullest potential. On the other hand, if the key is left in the accessory (“ACC”) position, the electrical system may be energized — but the battery will be dead when you get to your destination. Accessory items like a battery disconnect, fuse bypass or charge line kit may solve these problems (see the “Dinghy Accessories Guide” elsewhere in this issue for specific examples).

Before the wiring job is started, Roadmaster techs lay out the components of the kit in the cargo area, along with any necessary tools. Since the job starts with the taillights, this is a good way to stay organized and keep everything within reach.

To see what is involved in a basic wiring job, we recently stopped by Roadmaster, Inc. in Vancouver, Washington, and observed as its technicians installed the company’s Economy Wiring Kit (Part #152) in a customer’s 2017 Chevy Equinox. The kit includes a 27-foot length of four-wire electrical cord; 3 feet of split wire loom; a ring terminal, cable ties and wire connector. The kit also includes four of the company’s Hy-Power diodes, which prevent electrical “backflow” from the motorhome’s electrical system to the dinghy (and vice-versa), which can cause damage to both vehicle systems. The same vehicle also received some of the company’s accessory products, which lengthened the overall installation time — but in most cases, a kit like this should not take more than 2-3 hours for do-it-yourself RVer to handle with the right equipment (wire cutter/stripper/crimper, basic hand tools). Remember that universal kits like this one may require some modification or variations to the instructions depending on the vehicle, so your install time may vary.

Making any dinghy vehicle safe and legal for travel has never been easier, but when in doubt, always contact the manufacturer of your choice for advice, specifics and recommended accessories to make sure you get the job right the first time.

The first step is to remove the screws that secure the taillight assembly, then unplug the harness and place the tail light assembly aside.

Lengths of wire from the kit are assembled for each taillight, then strung down through an existing hole at the bottom of the housing. Most vehicles have holes like these in the housing to allow water to drain.

A test light is used to determine which of the wires in the harness provide power to the running lights and brake/turn signals. The harness is then cut. It will be spliced back together in a later step.

For this application, spade connectors were then crimped to the ends of the wires. The diodes are then plugged inline.

This harness is now finished and the taillight assembly is ready to be re-installed in the housing.

Wiring from both taillight assemblies is brought down through the respective drain holes in the housings, then routed over to the driver’s side and placed in a single loom. The stray white wire will be for the ground underneath the vehicle.

The wiring is then strung down the driver’s side, and secured to existing hard lines underneath the vehicle with nylon cable ties. The wiring is shielded and will not pass near the exhaust, so no further protection is required.

The wiring is routed through the bottom of the engine compartment and terminates at the front of the vehicle in the lower air dam. The red wire is for a charge line kit (sold separately), which was also installed.

The charge line wire goes into the center post on the back of the Roadmaster receptacle; it will connect to the vehicle’s positive battery terminal to keep the battery charged while the vehicle is in transit. The rest of the wires are inserted into the back of the receptacle one by one (see lead photo); each terminal is labeled so you know which wire goes where. Small set screws hold the wires in place.

Here, the receptacle has been wired up. Don’t forget to slide the protective rubber boot up the loom before you insert the wires into the receptacle, or you’ll have to do it all over again!

A generous amount of silicone is then applied to the back of the receptacle. While the silicone is still wet, the rubber boot is then slid down the wires and into place, creating a weathertight seal.

Here, the receptacle (left of the base plate arm) has been mounted to the baseplate bracket and is ready to accept the power plug from the motorhome.

Sources:

Blue Ox
(800) 228-9289
blueox.com

Demco Products
(866) 543-3626
demco-products.com

Hopkins Towing Solutions
(800) 835-0129
hopkinstowingsolutions.com

Roadmaster, Inc.
(800) 669-9690
roadmasterinc.com

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