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Trailer Lighting and Braking

Light and wiring systems need to be installed on a tow vehicle before it can tow a trailer. Every style of tow vehicle and trailer will have different set ups. Most trailers are wired to use a single red light for both the brake and turn signals (1 bulb per side). This is known as a 4-wire system.   Most import and newer domestic vehicles now have both a red brake signal and an amber turn signal. This is a 5-wire system. Tail light converters are necessary in this situation.

Due to newer computer systems also being added to vehicles special converter units and wire harnesses need to be added to bypass the computer system. Improper wiring can lead to blown fuses and overheating of the wires.

If a trailer is longer than 15 feet or weighs more than 1500 lbs it must come equipped with a brake system. Two different brake systems are used today.

  1. Hydraulic
  2. Electronic


Hydraulic brakes are typically found in boat and water sports trailers. These have an independent system activated by a master cylinder at the junction of the hitch and trailer tongue. The master cylinder is in this location so that any vehicle can tow the trailer. The inertia force of the tow vehicle’s braking action activates the master cylinder in the surge coupler, causing the brakes to be activated.


Trailer brakes are activated by the use of a brake control box mounted under the dash of the towing vehicle. This kind of brake system involves additional wiring to tie in the braking system and better power to the rear plug, which activates the trailer brakes when you press the brake pedal. A brake control box allows for brake control manually in an emergency or if you want to add extra braking action separately from the brake pedal.

What is a Breakaway Switch?

Breakaway switches automatically engage the trailer brakes if the trailer is accidentally detached from the tow vehicle. The switch uses a large dry cell battery or the auxiliary 12-volt battery contained within the tow vehicle. A pin is inserted into the breakaway switch to hold the switch open. If the trailer becomes detached, the cable will pull the pin from the switch which will then activate the brakes. A breakaway switch should never be used as a parking brake. This will cause the battery to drain and the switch will not work when needed.