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Tow Bar Wiring: Which Wiring Kit is for You?

To legally flat tow your vehicle you must ensure that it is properly wired and connected to your RV. Your towed vehicle's signal lights must act in accordance with the brake and turn signal lights on your RV or tow vehicle. There are four basic ways that you can achieve this:

Removable Tail Light Kits

If you only tow your car every once in a while, a removable light kit is probably the best. The least invasive of the tail light wiring kits, removable lights won't affect your towed car's electrical system at all. These self-contained add-on lights mount on your towed car and connect directly to your RV. Wiring is routed beneath your towed car up to your RV and is then connected to your RV to get the signal lights required. Upon receiving signals from your RV, they function as brake, running and turn signal lights.

Magnetic Removable Light Kit


  • Bypasses towed car's wiring system
    • No cutting, splicing or tapping required
    • 4-Way connector plugs into your RV's trailer connector
  • Installs and removes quickly and easily
  • Provides universal fit - use with any towed vehicle


There are a couple of different ways that these add-on lights can attach to your vehicle.

Magnetic tow lights typically sit atop your towed car's trunk or roof, whichever offers the best visibility and most secure positioning. The bases of these lights have heavy-duty magnets that are designed to stay firmly in place on your towed vehicle's exterior.

Trunk-mount lights function the same as magnetic tow lights, but instead of mounting on top of your trunk, they are closed into it. Each of these lights has a bent bracket that is designed to sit around the lip of your open trunk. To secure the lights, simply close the trunk and the bracket will remain between the edge of the trunk and the lid.

Tips for using removable tow lights:

  • Thoroughly clean the areas that magnetic lights mount to. If dirt and dust particles get trapped between the lights and your car, scuffs and scratches may occur.
  • Secure any loose wires to prevent them from blowing around while you are on the road.
  • Attach lights to a highly visible area at the rear of your towed vehicle.

Bulb and Socket Kits

A bulb-and-socket kit offers a more permanent solution for wiring your towed vehicle. Installation involves mounting a separate bulb and socket inside each tail light housing of your towed car. These bulbs will serve as your towing lights. Wiring is routed beneath your towed car up to the front and then connects to your RV to get the signal lights required. You need 1/4" space of clearance between the bulb and the lens.

Tail Light Bulbs for Dinghy Wiring


  • Bypasses towed car's wiring system
    • No cutting, splicing or tapping required
    • 4-Way connector plugs into your RV's trailer connector
  • Remains on vehicle - no need to repeatedly set up and remove
  • Offers clean look with no visible wiring


  • Access tail lights either by temporarily popping out the housings or by removing an access panel in your rear cargo area
  • Cut or drill access holes in the tail light housings for the light bulb bases and harnesses
  • Mount bulbs and sockets in housings and run wiring beneath your towed car to the front

Tips for using bulb-and-socket kits:

  • There must be enough room inside your towed car's tail light lenses for the additional bulbs
  • The holes in the tail light housings for the bulbs and sockets must be sealed properly to prevent moisture buildup
    • Condensation inside of the housings can lead to shorts

Hardwire Diode Kits

Diode Wiring Kit

The traditional method of wiring your towed vehicle to ensure that its signal lights will act in accordance with your RV's lights while it is being towed, is to use a diode kit. This method requires a more involved installation process, but once complete you never have to re-mount, set up or manually activate a thing.

Hardwire diode kits can include:

  • 4 Diodes for 2-wire systems (or for a 3-wire towed car that you intend to wire as a combined system)
  • 6 Diodes for 3-wire systems
  • Single block-style diode for either 2-wire or 3-wire systems

Kits that include either four or six diodes that splice into your towed car's wiring are the most common tail light wiring kits.

Wiring Diode


  • One-time setup
    • Remains in place, at the ready between trips
    • Activates automatically when you hook towed car up to RV
  • "Hidden" system is out of sight beneath your vehicle
    • No visible wiring
    • No extra bulbs or add-on lights
  • No electrical feedback
    • Won't damage towed vehicle's electrical system


Installation of diodes can be rather involved. Watch a video demonstration of this process to get a better idea of the installation procedure.

Combined versus Separate Lighting

You must splice into your towed vehicle's wiring to install diodes. They are designed to be connected in line with the car's circuits. To determine exactly how this is done, first you need to know what type of lighting system your car has.

Combined or 2-Wire Lighting System

  • Brake and turn signals travel along same wire
  • Brake lights do the flashing for turn signals

Separate or 3-Wire Lighting System

  • Brake and turn signals travel along separate wires
  • Turn signal lights are separate from brake lights, and are typically amber

Once you have determined the type of lighting system your vehicle has, you can begin installing your diodes. Detailed instructions on how to splice diodes into your towed car's existing wiring can be found in the following articles:

  • Diode installation instructions for a combined dinghy
  • Diode installation instructions for a separate dinghy

Block Style Diode

Block-style diode kits are also available. Installation with a block diode system is less complicated, but may be more time consuming because you must find a place to mount the block where all of the wires can reach. With the block diode system you can wire your towed vehicle as either a combined or a separate system.

Tips for using hardwire diode kits:

  • Most diode kits include a 4-way vehicle-side connector. A 4-way connector is only capable of transmitting along a 2-wire system. If you want your towed vehicle to maintain its separate lighting, then you must do one of the following:
    • Install a tail light converter to break the combined signals from the 4-way into separate signals to be sent to the tail lights
    • Replace the 4-way connector with a 6-wire connector that is capable of carrying all of the signals separately
  • You can wire your 3-wire vehicle to operate as a combined system by using a 4-diode kit to minimize installation time and hassle.

Custom, Plug-In Wiring Harnesses

The newest and simplest way of wiring your vehicle to be towed is to use a custom-fit wiring harness that plugs into your tow vehicle's existing tail light wiring harness. These custom harnesses function just like the diode systems, but require no cutting or splicing of wires.

Plug-In Tail Light Wiring Kits


  • One-time setup
    • Remains in place, at the ready between trips
    • Activates automatically when you hook towed car up to RV
  • Vehicle-specific plugs connect to your tail light wiring harness quickly and easily
    • No cutting, splicing or tapping
  • "Hidden" system is out of sight beneath your vehicle
    • No visible wiring
    • No extra bulbs or add-on lights
  • No electrical feedback
    • Won't damage towed vehicle's electrical system
  • No need for a tail light converter


  • Locate your vehicle's tail light harness - typically just behind the tail light assemblies
  • Plug the custom harness in line with your existing harness
  • Run the wiring up to the front of your vehicle and mount the vehicle-side, 4-way connector

TowDaddy LED Troubleshooting Module

The control module on the TowDaddy wiring harness has built-in LEDs to help with installation. These lights ensure that you install the system correctly and also make for fast, easy troubleshooting.

Hook up to your RV to power the TowDaddy and make sure that the...

  • Green lights illuminate when the tail lights are on
  • Red lights illuminate when the brake lights are on
  • Yellow lights illuminate when the turn signals are activated

Tips for using custom, plug-in kits:

  • Go through our tow bar wiring application guide to determine which harness will fit your vehicle
  • TrailerMate harnesses combine your brake and turn signals so that they travel along the same wire, regardless of how your vehicle is designed. As a result your towed vehicle's brake lights will not only act as brake lights, but will also flash to act as the turn signals.
  • TowDaddy is able to maintain your towed car's 3-wire system. That being said, this harness does not, strictly speaking, maintain your vehicle's separate functioning. Both the brake light and the turn signal light will remain separate, but they will illuminate in tandem.
    • If you depress the brakes in your RV, both the brake lights and turn signal lights will burn solid.
    • If you activate the turn signal, both the brake light and turn signal light on the side to which you are turning will flash.

Angela B.


there's so much information on how to wire your RV to the towed vehicle

Raymond D.


My tow dolly has lights with a 4 pin plug that attaches to my 7pin RV adapter plug. I want to light up my dinghy for more visibility. What kind of RV 7pin adapter plug do I need to have both sets of lights working???

Etrailer Expert

Jon G.


What I'd do is use the Hopkins Adapter # 37185. Replace your current RV 7-Way with this so that you can use the 7-Way like you are currently using it and then you have the 4-Way plug as well. You could even install wiring like the Flexo-Coil # RM-15267 if you're wanting to add a wiring kit that installs right into your OEM wiring. Just be sure this is good to use with your vehicle.

Damase B.


I purchased plug in harness from you to tow behind my 07 Suzuki sx4 and now I am wondering if I can backfeed from my motorhome when I am towing the Suzuki as a dinghy by running a set of wires from the motorhome to the trailer plug just installed.

Etrailer Expert

Chris R.


I believe you're saying that you have a trailer harness for the Suzuki (to use for trailer towing) and are wondering if you can tap into that same harness to power its signal lights while the Suzuki itself is being towed. If that's not correct just let me know. Unfortunately there's not a good way to do this. You'll need to add a totally separate wiring kit like the Roadmaster # RM-15267 or go with a more temporary setup like the Magnetic Light Kit # TL21RK.



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