How to Install Load Resistors for LED Turn Signal Lights:

To add a load resistor to an indicator (turn signal) it has to be wired into each LED light bulb in parallel. I.e. The load resistor goes across the light bulb connections, between the supply and ground.

A load resistor is required for each LED light bulb in the turn signal circuit, (you may only want to upgrade the rear of the vehicle? In which case you only need 2 x load resistors).

50W 6 ohm Load Resistor
50W 6 ohm Load Resistor

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Precautions:

  • Any installation is at your own risk. Each vehicle may be different, or may have been previously modified.
  • Disconnect the battery, when wiring vehicles.
  • If you’re unsure, use a qualified auto electrician. As modern vehicles electronics can be damaged easily.

Don’t forget, load resistors can generate lots of heat, so position carefully.

Video: Install a Load Resistor for LED Lights.


LED Resistor Wiring Diagrams:

LED Turn Signal Load Resistor Wiring Diagram (Turn Signal Only)
LED Turn Signal Load Resistor Wiring Diagram (Turn Signal Only)
LED Turn Signal Load Resistor Wiring Diagram (Stop/Turn Signal)
LED Turn Signal Load Resistor Wiring Diagram (Stop/Turn Signal)

A typical load resistor for a 21 watt turn signal light bulb would have a rating of 50 watts, 6 ohms. Though please check with your supplier.


Calculating the Size of a Load Resistor:

To someone familiar with electronics, calculating the size of a load resistor may be easy. But to anyone else, it could be a bit confusing…

Therefore I’m not going to try and explain in too much detail, but just give an understanding of how the size is calculated.

The load resistor replaces the load lost when the filament light bulb was replaced by an LED light bulb.

In other words:

Load Resistor Calculation
Load Resistor Calculation

You can use calculations to obtain the size of the load resistor.

First we need to calculate the difference between the filament light bulb and the LED light bulb in watts:

A = The size of the filament light bulb (in watts).

B = The size of the LED light bulb (in watts).

The difference = A – B

Using Watt’s law and difference between the filament light bulb and the LED light bulb (in watts) calculated above, we can find the current (amps) needed to mimic the filament light bulb.

Load Resistor Calculation (Current)
Load Resistor Calculation (Current)

We will then use the current (amps) calculated above to find the resistance (Ω or Ohms) of the load resistor.

Load Resistor Calculation (Resistance)
Load Resistor Calculation (Resistance)

The resistance and the number of watts are the two parameters needed for obtaining the size of the load resistor.

The wattage of the load resistor is the value used in the calculation above…

The filament light bulb (watts) The LED light bulb (watts).

This will give you the lowest wattage figure, but the load resistor will get very hot (just like a filament light bulb). So the heat needs to be dissipated using a much larger wattage load resistor (at least double).

One of the problems with this calculation, is often the LED light bulb specification isn’t readily available, or is a bit vague. Which then makes calculations difficult (guesswork).

Researching on the internet, it seems a typical load resistor to replace a 21 watt turn signal light bulb would use a 50 watt 6 Ω (ohm) load resistor. Note the 50w rating to dissipate any heat.

A good supplier of load resistors should also be able to advise and assist with your selection, if you are unsure what to purchase.


Buying LED Lights & Load Resistors:

If you’re not sure what you want, sometime you have to look to see what is available? The list below may give you some idea of what’s available to buy…

LED Load Resistors & LED Lights

Item Location Link
Load Resistors AUS https://ebay.us/UnwmJS
CAN https://ebay.us/kdJK2s
FR https://ebay.us/q76FId
IRL https://ebay.us/RJ9TvT
UK https://ebay.us/EIbSeN
USA https://ebay.us/XRTwiT
LED Lights AUS https://ebay.us/yuFGjn
CAN https://ebay.us/FCY9AO
FR https://ebay.us/32HIS5
IRL https://ebay.us/bu0XGw
UK https://ebay.us/SzlZvB
USA https://ebay.us/5ykO5i
Disclosure: The links in this table are “affiliate links” This means we may garner a small commission (at no cost to you) if you choose to make a purchase.
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