Often considered an after-thought for many vehicle owners are trailer lights and the wiring for the required vehicle operating them, especially for small utility trailers. In all jurisdictions in Canada, when towing a trailer, it is required to have operating running, brake, signal and reverse lights (dependent on size). Often drivers think that if their trailers are visible over a low-profile trailer, operating lights on the trailer are optional. There are a few important things to know when it comes to wiring your vehicle with the necessary connectors to power these lights.

Many of the newer vehicles today have a lot of electronics connected to exterior light. This could be one bulb for brake, running and signal functions. Equally so many makes and models use separate bulbs for these different functions. Then to throw an additional curveball are the vehicles whose lights are controlled by a computer. Now how does this affect trailer lights you ask?

A special plug goes into the trailer connector for the rear trailer camera. JIL MCINTOSH / DRIVING.CA

An electronic adapter box is needed to convert voltage signals for most applications that have a separate bulb for the brake and turn signal function, into something the standard four-pin trailer wiring connector can use. Prior to installation of this adapter, determine if it requires its own dedicated power supply from the vehicle’s battery in order to function. If this is the case it will require undercarriage circuit routing installation of a very long black-coated wire.

One of the greatest dislikes of these adapters are amperage spikes. Anything more than a three-amp spike, for even the best aftermarket brands, will blow the adapter box and trailer lights will cease to function. Even a factory-installed or dealer-sourced accessory kit can experience the same problem. This alone makes annual trailer light and wiring harness inspection crucial – especially for any trailer that sees even one Canadian winter.

First step is to remove each light lens, being mindful to not tear any rubber or foam gaskets. Remove each bulb checking its base and the lamp’s socket for any sign of corrosion. Brushing the base with a small wire brush should remove most build-ups. Before re-inserting the bulb, wipe a small amount of di-electric paste or gel on each contact. Look for insulation wrap cracks or breaks or any loose or exposed connectors by tracing each lamp’s wiring harness from the lamp base to the connector at the front of the trailer. Also make sure the trailer plug that connects to the vehicle is corrosion-free and clean.

Harnesses and lamps in need of service can cause more problems than just inoperative trailer lights. The most common being an anti-lock (ABS) warning light turning on when the trailer’s wiring is connected to the vehicle. As most ABS systems are protected against external electrical faults, so they should reset to operational when the trailer is disconnected and the wiring or lamp fault is repaired.