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Trailer lights and the required vehicle wiring to operate them are often considered an after-thought for many vehicle owners, especially for small utility trailers. Many times, drivers think that just because their taillights might be visible over a low-profile trailer, operating lights on the trailer are optional. Yet in all jurisdictions in Canada, if you are going to tow a trailer, it must have operating running, brake, signal, and (dependent on size), reverse lights. When it comes to wiring up your vehicle with the necessary connectors to power these lights, there are a few important things to know.
On many of today’s vehicles, there are a lot of electronics connected to exterior lighting. Many times, one bulb is used for brake, running, and signal functions. And there are an equal number of makes and models that use separate bulbs for these different functions. And of course, more and more vehicles have their lights controlled by computers. So, what’s this got to do with trailer lights?
For most applications with a separate bulb or lamp for the brake and turn signal function, an electronic adapter box is needed to convert those voltage signals into something the standard four-pin trailer wiring connector can use. Many times these adapters require their own dedicated power supply from the vehicle’s battery in order to function. If the correct trailer wiring kit for your particular make and model requires such a continually powered adapter, you’ll usually find a coil of black-coated wire that’s about as long as the length of your vehicle, meaning getting a little down and dirty with undercarriage circuit routing installation is necessary.
The deal with these adapters is their intense dislike of amperage spikes. For even the best aftermarket brands, anything more than a three-amp spike will blow the adapter box and the trailer lights will cease to function. And even a factory-installed or dealer-sourced accessory kit may experience the same problems. This makes an annual trailer light and wiring harness inspection a must for any trailer that’s seen even one winter.
Start by removing each light’s lens, being careful not to tear any rubber or foam gaskets. Pop out each bulb and check its base and the lamp’s socket for any sign of corrosion. A light small wire brush will easily take care of most build-ups. Before reinserting the bulb, wipe a small dab of di-electric paste or gel on each contact, just enough to provide a thin coat (available at any parts store). Carefully trace each lamp’s wiring harness from the lamp base to the connector at the front of the trailer to look for insulation wrap cracks or breaks or any loose or exposed connectors. Make sure the trailer plug that connects to the vehicle is also clean and corrosion-free.
Inoperative trailer lights aren’t the only problem that harnesses and lamps in need of service can cause. They can lead to various vehicle system faults with the most common being an anti-lock brake (ABS) warning light popping on when the trailer’s wiring is connected to the vehicle. 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.
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