Wiring is often a dreaded task thought to be too complex for an average homeowner but in reality it’s a simple concept and wiring a trailer can be done by a beginner in about 2 hours. Whether you’re wiring a homemade trailer or replacing the wiring on an old or damaged trailer, the tips and wiring diagrams below will make quick work of your project.
Wiring a trailer (or a car/truck) is very similar to wiring a house – each device (light) has a positive and a neutral connection. There are two main differences between automotive and residential wiring;
- Automotive uses a 12vDC system whereas residential homes use a 120/240vAC system.
- Automotive wiring commonly uses the frame as a neutral, taking advantage of the metal frame to eliminate the need for a second wire at each device. Since copper is expensive, this is a significant advantage. It’s important to ensure continuity (uninterrupted flow of electricity) between all components of the trailer which we’ll talk about below.
We’ll cover the basic 4 wire system but the processes are the same for 2,5,6 and 7 wire systems, simply refer to the wiring diagrams at the base of this article. We won’t cover electric brake wiring here due to the increased complexity and critical importance of an effective braking system. We recommend seeking the help of a qualified professional when re-wiring, installing or adjusting any brake system.
To complete wire your own trailer you’ll only need a few basic tools and your materials.
- Wire Stripper/Crimper
- Drill Bits (assorted, small)
- Screwdrivers (assorted)
- Circuit Tester*
- Trailer wiring plugs to match required inputs and vehicle output.
- Coloured wire. This often comes in a spool with 4-5 wires and the 4-5 pin connector attached. While coloured wire isn’t required it makes the wiring process much easier.
- Wire clips/straps/staples
- Terminals (tube, ring & blade)*
- Terminal (dielectric) grease*
- Electrical tape*
- Abrasion resistant loom (woven or split loom is optional but should be used any time there is a possibility of the wire chaffing against the trailer frame resulting in damage to the wire insulation)
*Note: all of these items are available in kits such as the Hopkins 51000 kit which includes a 12v LED circuit tester.
Tips & Tricks
- Remember each set of lights must have a dedicated circuit (ie. left turn signals are all tied to one left-turn circuit.
- Use the circuit tester to ensure continuity between all non-welded components as corrosion or gaskets can sometimes interrupt the flow of electricity in bolted connections. The bolt upon which tilting trailers pivot is sometimes found to have a bushing or corrosion build-up. If a reliable bond cannot be made a short jumper may be used, made of two ring terminals and a short length of wire, bolted directly into the frame of each component.
- Trailer lights may have 1, 2 or 3 connections depending on design and purpose.
- 1 connection lights with an integrated neutral. Some lights have integrated neutral connections which are connected to the trailer ground via the mounting screws. Alternatively, some lights have designated terminals for neutral connection.
- 2 connection lights may either be a dual purpose light (ie. stop and turn signal in one unit) with an integrated neutral, or, a single purpose (standalone brake light or a standalone amber marker) without an integrated neutral.
- 3 connection lights have two load terminals for two independent functions (ie. stop and turn signal in one unit) and a neutral terminal.
- Neutral terminals of each light must be bonded to the frame to complete the circuit and operate the light.
- Tally the loads from each device to ensure the current doesn’t exceed the allowable level for the size, type and environment of the wire.
- If you’re using non-coloured wire it’s easier to finish a complete circuit before beginning another to eliminate confusion between similar wires.
- Use dielectric grease on all non-permanent connections. Also called terminal grease, this keeps water from infiltrating and corroding connections. The dielectric property is important as the grease is non-conductive and won’t lead to faults or short-circuits.
The below chart from Hopkins outlines the purpose of each wire within the common connectors. Rely only on the wire position as wire colour is vehicle-specific.