To ensure safe towing, you must make certain that your vehicle and trailer are outfitted
with WORKING running and signaling lights.
By law in every state, a trailer must have running lights, tail lights, and or marker
lights, turn signals, and brake lights. To add a trailer light adapter, you must tap
into the tow vehicle's electrical system and transfer it's power to the trailer wiring
Warning: Be aware that some manufacturers, such as
Cadillac, Lincoln, Dodge, Jeep, and many luxury imports require a special wiring system
that is included in the Towing Package. This wiring system has a built in sensor to
prevent electrical damage to the onboard computer that monitors the vehicle's
standard light system for faults. If you are wiring a vehicle that has such a
system, kits are available that connect directly to the vehicles battery, not to the
vehicle's wiring. Be careful, computer repair is expensive!
Note: If hooking in trailer lights to the
wiring under the vehicle, avoid using 3M style quick pinch connectors. The metal prong
pierces the plastic coating of the wire and lets in water and road salt that eventually
destroys the wiring loom on the vehicle.
Electrical power is transferred to a boat trailer by using a four-way connector.
One pin in the connector transfers power to the running lights, two others power the turn
signals and brake lights. The fourth pin is for supply and electrical ground. A
tow-vehicle connector is often included when you order a vehicle with the ''Towing
Package." Otherwise you'll need to install one. (Most new boat trailers come with the
correct plug from the manufacturer of the trailer, and the selling dealer will often
install one for you.)
The most common connectors for boat trailers are flat plugs. But, they generally
dangle from the rear of a tow vehicle and scrape on the ground. Many boaters wrap the
connector wiring around hitch parts, but this causes the wire to crack and create
electrical shorts. The best way to correct this is to install clips that hold the plug
securely to the tow vehicle without twisting the wire. These are available from many hitch
Another connector option is a round, plated, four-way plug. It is permanently
attached to the vehicle and has a lid to keep the connectors inside clean. However, should
the connectors get dirty, they're not as easy to clean as plastic flat plugs are. With a
plastic plug; a few in-and-out, twisting motions with the pronged part of the connector
will free the open plug of dirt and corrosion. With the round connector use contact
cleaner to do the job and to keep the door lid from sticking.
Note: When wiring for the best fit between tow
vehicle and trailer, be sure to leave enough slack in the wiring for tight turns.
Otherwise, you'll disconnect or tear the wiring. Also, never wrap or drape the wiring
over the hitch or ball of the vehicle because the coupler from the trailer could
pinch the wire in turns.
Many people tow more than one kind of trailer, so today's towing packages often include a
wiring adapter. This eliminates the need for wiring multiple connectors to the tow
vehicle. These adapters can also be found at trailer dealers and hitch-installation
Most adapters include four-plug and seven-plug access. A seven-plug adapter is mainly used
for travel trailers that need power for refrigerator and electric-brakes. Some even use
If you tow two trailers, each with different wiring systems and connectors you may need an
additional adapter. Generally, the main plug is a seven-way connector. To this, you insert
a four-way or any other size that is needed for the application.
Many automotive manufacturers require that the factory turn signal flasher be replaced
with a heavy-duty "flasher". The flasher controls how the turn-signal
lights "flash". The standard flasher that comes with most vehicles is not
designed to operate more than vehicle's lights, so it overloads. This overloading causes
the tow vehicle and trailer turn signals to flash rapidly and faintly, so they are hard to
see by motorists driving behind you. Changing to a heavy-duty flasher will solve the
problem. Be sure you get the right heavy-duty replacement, make sure it is designed for
trailering applications. All flashers are calibrated to the amperage required and
the number a light bulbs on the circuit.
The flasher is usually located under the dashboard. On most new vehicles, it is connected
to the fuse box and simply pulls out. There are usually two flasher modules, one
flasher for the turn signals and one for the emergency lights. You should only need to
replace the turn signal flasher module, although we recommend testing the emergency
flashers as well.
Wiring flat, four way plugs is based on a standard color code used by GM and others.
(Ford, as well as others, color codes are different) Brown is for taillights and
side marker lights. Yellow is for the left-turn signal and brake light. Green is for the
right-turn signal and brake light. White is for electrical ground.
Round, four-way plugs don't always have a consistent color code, and often come without
any wire at all, so you will have to use a 12 volt test light to map the socket lay out
and install wires color coded and of sufficient gauge for your application.
Note: Always use a 12 volt test light and
a volt meter, when doing any trailer wiring or troubleshooting. ( Just take my word for
All foreign vehicles, and several American ones, use an "international" lighting
system. This means that the turn-signal lights are separate from the stoplights. If the
lights on the rear of the vehicle have an amber lens for turn signals and a red lens for
stoplights, you need a converter. The "American" lighting system combines the
turn signal and stoplight functions into one wire instead of two.
American boat trailers use the "American" lighting system. Consequently, if the
tow vehicle has an "international" system, the two separate wires for turn
signals and stoplights, on the tow vehicle, must be combined into one. To do this, a
converter is necessary.
A converter is a circuit board built into a small, plastic, waterproof box or built
directly into a four-way connector. The one built into the converter is preferred, because
it reduces the number of wires needed to activate it, and it is not necessary to have a
separate box that needs to be mounted elsewhere. Usually, three or four wires from the tow
vehicle left and right turn and brake wires go into the converter and two wires come out.
The two wires coming out are connected to the left and right turn connectors in the
Always check all lights before you leave home. If they don't work, the most likely cause
is dirt or oxidation on the contact points. So, be sure that all connector plug prongs and
receptacles, light-bulb sockets, wire splices and ground connections to the trailer are
clean, oiled, and shielded from moisture. A little light waterproof grease or engine
fogging oil spread on the surfaces will act as a barrier against air and moisture, retard
oxidation, and keep the lights operating longer.
· It's best to solder wire-to wire splices, then wrap them tightly with plastic
electrical tape, or better still, with heat-shrink tubing, it will help seal out dirt and
moisture. Crimp connectors work for a while, but eventually corrosion forces you to cut
them out and replace them.
· Make it a frequent habit to scrape the prongs clean with a pen knife or sandpaper. Try
to scrape off any surface deposits in the connector holes with an small file or small
piece of sandpaper rolled around a toothpick (be sure the lights are off when you do this,
otherwise it could blow a fuse). Then, dab a little grease on the prongs, push the
connector together and wrap electrical tape around the crack to keep out dirt and
· Between uses, keep both halves of the plug protected from weather and scuffing. To keep
dirt from getting into the connecting plugs; wrap the plug with a small. plastic bag
slipped over the top of each half. Then wind a rubber band around the open end to seal it.
You can also use an old plug, greased and with the wires cut off, to plug into the one on
the car as a way to protect the plug from damage.
In either case it is advisable to replace the light adapter, that hangs under the vehicle,
every couple of seasons, if the car is driven in northern climates where salt is used on
the highways to keep them from icing. The road salt has a nasty habit of permeating the
wire itself and electrical resistance can increase dramatically in a very short time.
AS A SIDE NOTE
Always disconnect the trailer wiring and give the lights a chance to cool down
before launching or retrieving a boat. The trailer bulbs get very hot, so when the lights
touch the cold water, there's a good chance of them popping. Though a bulb change may not
seem a major catastrophe to some, if the taillights are sealed units, you will have to
replace the entire light assembly. Plus, you won't have any trailer lights when you return