When converting a vehicle for use with LED Turn Signal bulbs, it is often not enough to simply replace the regular incandescent bulbs with LED bulbs. In many cases, you will have to either replace the car’s flasher module, or trick the flasher module into thinking that there are “regular” bulbs in your car…
…and here is why:
An LED bulb only consumes a very small amount of electrical current. The turn signal flasher (if it’s a regular “thermal” flasher) was designed for bulbs that consume a lot of power: The power consumed by the bulb runs through the flasher and heats up a bimetal switch. When the bimetal deforms from the heat, it breaks the circuit (causing your lamp to go off), this causes the switch to cool down and go back to it’s original shape (it will close the circuit again, the lights come on, the switch heats up, and the cycle begins again).
If the amount of power going though the switch is very little, not enough heat is generated in the flasher to cause the bimetal to bend. The most common symptom is that your turn signal lights simply stay on. If you run a MIX of regular and LED bulbs (say regular in the front, LED in the back), you may not notice it but if your incandescent bulb breaks, you’re back to nothing-flashing.
Other symptoms are fast flasher, slow flashing or not coming on at all.
There are usually two solutions:
Install Load Resistors: these resistors basically a resistor that consumes enough power to cause the stock flasher module to kick in. Your flasher basically doesn’t know that you’re running LED bulbs. This is usually the more expensive solution, creates a lot more work and just generally undesirable. However, this may be what you have to do if you cannot find an LED-compatible flasher.
LED-Compatible Flasher: This will work on most cars (and the older the car, the more likely), and usually means ripping out the stock flasher and putting in an LED-compatible replacement. Sometimes you may have to flip some wires (and you can find harnesses to make that really easy). There are various different models of LED compatible flashers, and there are also different types.