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Taillights/Marker Lights Not Flashing or Rapid Flashing

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Taillights/Marker Lights Not Flashing or Rapid (Hyper) Flashing

For some vehicles this is a common problem after updating the tail lights and/or other signal lights to LED/SMD bulbs.  We recommend a couple different ways to address this problem, but first it is important to understand why there is a problem. 

The Problem: 

The reason that the turn signals suddenly stop working after LED or SMD bulbs are installed has to do with the load put on the signal flasher relay.  In many vehicles, the signal flasher is a thermal flasher design.  This type of signal flasher relay work by heating up with the current for the bulbs passes through the relay.  When it reaches a certain temperature, it shuts off until it cools down.  Once it is cooled, it turns on again until it reaches its shut off temp.  The cycle of heating and cooling results in the lights going on and off at an interval, known as the blink rate.  

The amount of current drawn by the bulbs is required to properly activate the thermal flasher.  In some vehicles, when the load drops below the amount required by the flasher relay, the relay will not reach temp and the bulbs will not flash.  In some vehicles that have a “bulb out” feature, the flasher will increase the blink rate and make the bulbs flash rapidly to notify the driver that there is a bulb out in the system. 

The auto manufacturer selects a flasher for the vehicle that best matches the “load” created by the bulbs in the turn signal system.  In some cases, the load maybe very close to the minimum required to make the flasher cycle.  In other vehicles, the minimum load requirement may be much lower than the load created by the vehicle’s bulbs.  This is why some changes to LED bulbs, have no effect on the function of the system.  As long as the total load is in line with the flasher relay’s requirements, the system will function without any issues.

When bulbs are changed from the factory installed incandescent bulbs to LED or SMD bulbs, the current draw (or load) to the flasher is reduced.  One of the great benefits of LED bulbs is lower power consumption, but for vehicles that have thermal flasher relays installed, this will require some changes.   

The solution(s):

There are a couple of possible solutions to the problem.  The first and easiest way to correct the issue is to change the signal flasher relay to an electronic type signal flasher relay.  These electronic units replace the thermal design with a relay that detects a much lower load and begins and “electronic” cycle of open and closed circuit to create the blink rate.  Electronic Signal Flasher Relays are a simple and effective upgrade because they are a plug in replacement for the factory flasher.  Upgrading the signal flasher resolves the problems associated with LED conversion about 95% of the time.  They are the recommended solution to the problem, but they are not the only solution. 

The other alternative is to add in line load resistors to the turn signal system.  The load resistors increase the current draw of the signal system to bring the total load on the flasher back to within the signal flasher relay’s range.  Simply put, the load resistors draw additional current to create a stronger signal to the flasher relay.    The down sides to adding load resistors is that they get hot and they reduce one of the primary benefits of change to LED or SMD bulbs; less current draw.  That said, load resistors are a quick and easy way to fix a signal flasher problem. 

Although either of these solutions will remedy the problem, we recommend that you first install an updated electronic type signal flasher relays before attempting to add load resistors.  At a minimum, using an electronic flasher relays will reduce the size of the load resistor required, resulting in less heat and less current draw across the system.