LED turn signals are a popular modification, offering brighter, crisper light output and a modern aesthetic. Unlike filament bulbs, LEDs activate instantaneously, improving visibility. While upgrading is straightforward, successful implementation requires attention to regulatory standards and the vehicle’s electrical architecture. This modification is permissible, provided the new components are installed correctly and function in a compliant manner.
Legal Status and Road Compliance
The permission to use LED turn signals on public roads is governed by federal and state regulations, which dictate specific performance criteria. In the United States, the Department of Transportation (DOT) sets the Federal Motor Vehicle Safety Standard (FMVSS) No. 108, which applies to all vehicle lighting equipment. This standard does not prohibit the use of LED technology but requires that any replacement signaling device meets the mandated specifications for color, intensity, and visibility angles.
Turn signal color must be amber for the front and side; rear signals can be red or amber. The light must project with sufficient intensity and over a required field of view to be clearly seen by other drivers. To ensure compliance, aftermarket LED bulbs or assemblies should carry a DOT or SAE (Society of Automotive Engineers) certification mark. This certification indicates the product meets the necessary photometric standards. Using components marked “for off-road use only” can lead to violations, as they may not meet the required lighting specifications.
Addressing Hyperflash and Technical Requirements
The most common technical hurdle encountered when switching from incandescent to LED turn signals is a phenomenon known as “hyperflash.” This rapid blinking rate occurs because a vehicle’s turn signal circuit is designed to sense the power draw, or electrical resistance, of the original incandescent bulb. Traditional bulbs utilize a filament that draws a significant amount of current, typically around 21 to 27 watts, which the flasher relay expects to see.
LEDs are highly efficient and draw a drastically lower amount of current, often less than 5 watts. The vehicle’s flasher relay or electronic control unit (ECU) interprets this reduced electrical load as a burned-out bulb. The system initiates the hyperflash warning to alert the driver of this perceived fault. This safety feature must be bypassed for the LED turn signals to operate at the standard 60 to 120 flashes per minute.
There are two primary methods to resolve hyperflash and restore the normal flash rate.
Load Resistors
The first method involves installing a load resistor in parallel with the LED bulb on the turn signal circuit. A load resistor is an electrical component that mimics the resistance of the original incandescent bulb by drawing the necessary extra current. For a standard 21-watt bulb replacement, a common choice is a 50-watt, 6-ohm resistor, which draws enough power to trick the vehicle’s system. These resistors convert excess electrical energy into heat, requiring them to be securely mounted to a metal surface away from plastic components or wiring.
Flasher Relays and Canbus Solutions
The second solution is replacing the original flasher relay with a solid-state, LED-specific flasher relay. This electronic module is designed without the thermal or current-sensing components of the original relay. This allows it to maintain a consistent flash rate regardless of the low electrical load from the LEDs. For vehicles using a Controller Area Network Bus (Canbus), the preferred solution is often a Canbus-compatible LED bulb. These bulbs have small, built-in resistors that simulate the required load, preventing both hyperflash and dashboard “bulb-out” warning messages.