LED Light Load Resistor Wiring Steps Installation Tip

Installation Tip: LED Light Load Resistor Wiring Steps 

The procedures in this technical sheet involve electrical wiring and installation of LED light load resistors. Always consult the vehicle workshop manual to verify wire colors, circuits, and connections before making any electrical modifications. If you are unsure of any procedure, lack the proper tools, or are uncomfortable performing electrical work, do not proceed and seek out a qualified Classic British Repair Facility.

LED load resistors can become extremely hot during operation and may cause burns, melting, or fire if improperly mounted. Always secure the resistor to a suitable metal surface away from plastic, wiring, light housings, fuel or other heat-sensitive components. Do not operate the vehicle with an improperly secured or exposed resistor.

Incorrect wiring, improper connections, or the use of a polarity-sensitive resistor in the wrong configuration may damage the lighting system, resistor, wiring, or other electrical components. Insulate any unused wires and verify proper signal, brake, and tail-light operation, including confirming that the turn signals are not hyper-flashing, before completing installation.

The person performing the work assumes all responsibility for the use of the information contained in this document.

Safety and Mounting:

Mount to Metal: Load resistors get extremely hot (up to 170°C/340°F) because they dissipate energy as heat. Always mount them to a flat, metal surface of the vehicle’s chassis using self-tapping screws.

Avoid Plastic: Ensure the resistor does not touch plastic components, wires, or the light housing itself, as it can melt them.

Test Before Finishing: Turn on the signal to verify the operation of the signal and brake lights are correct. Confirm light is not functioning in the hyper-flash mode prior to re-installing your taillight assembly.

Single Bulb Setup

For a standard single-function socket, there are typically only two wires at the harness: one power and one ground.

Identify the Wires: (Reference workshop manual for correct wire codes and connection)

Locate the two wires going to your bulb socket. Usually, the black wire is the ground, and the colored wire is the power/signal. Since an LED load resistor is not polarity (positive/negative ground) sensitive in the way a diode or LED itself is. It will work the same in either direction no “positive side” or “negative side” requirement.   

Connect the Resistor: 

• Attach one wire from the resistor to the positive (power) wire of the bulb.
• Attach the other wire from the resistor to the negative (ground) wire of the bulb.
• Note: Standard load resistors are not polarity-sensitive, so it does not matter which resistor wire goes to which vehicle wire.

Use kits include T-tap or quick-splice connectors.

Addressing the "3-Wire" Resistor

If your resistor kit has three wires but you only have two wires at your bulb, it is likely designed for a dual-function bulb (e.g., a combined brake/taillight or park/turn signal).

Is a 3-Wire Resistor polarity sensitive:

• Pure resistors are NOT polarity sensitive
• Modules or smart resistors MAY be polarity sensitive

How to tell what you have:

• Plain resistor pack: no polarity, safe either direction
• Polarity sensitive resistor will have labels like + / – / signal: make sure you install the resistor in the correct polarity positive or negative  direction as it will matter in this case.

For single-function use:

• You will only use two of the resistor's wires. Typically, these are the red and black wires (acting as power and ground).

The extra wire: This is usually for the second circuit (the "dim" mode or marker light) and should be capped off or insulated with electrical tape if not used.