2008 Volvo S40. Has anyone installed LED headlamps (Low Beam, High Beam) on their S40? I am getting the warning light on dash (meaning I need to install resistors.) I believe the resistors get very hot so I do not want to leave them inside the sealed headlamp assembly. Has anyone come up with a work around? Thank you!

 

Resistors get hot because that is how they work, they turn electrical energy into heat energy, like a lightbulb. Resistors are needed to trick your car into seeing the correct wattage usage as LED use less watts to generate light. Heat generated by resistors = watts.

 

Yes, I am aware of how resistors work and that they are supposed to get hot. I was asking the question to see if anyone has done a modification to the headlamp assembly to allow for use of LED's and resistors, or if there is another option. Thank you for the response.

 

I see, you can potentially run the resistor before the bulb prior to the headlight assembly. I have seen some others do that before, not on an S40 though, but the wiring should be similar. You would just need to figure what values you need for the resistor. There may even be plug and play parts online that plug into bulb socket and just remove the plugs so you dont have to keep it internal.

 

I did see a plug and play on a YouTube video where the installer just dumped the resistor into the headlamp assembly. Not sure I want to "test drive" whether or not it will melt the inside of my housing. Will keep searching for a potential solution. Alla lighting claims they have a bulb that is a higher wattage that will not trigger the warning light. Will give it a try and see. Thanks again!

 

Its a little more difficult on the 2004+ cars because the CEM reads the resistance coming back from the light to determine if it is working properly. The older ones used a resistor shunt that you could drill a particular size hole into and change the readout.

Another option is to put a hole in the back cover of the headlight and keep the resistor on the outside and seal it back up. wouldnt look pretty but it is an option.

 

You can put the resistor on the outside of the headlight housing - just wire it across (aka "in parallel with") the wires going to the bulb(s).

Figure that the H11 low beam bulb draws 55 watts. Figure that the LED replacement will use 10 watts.

That means you need to "burn off" about 45 watts to keep the computer from thinking your headlight bulb is burnt out.

At 13.8 volts (nominal running voltage) you will need to draw 3.26 amps to dissipate 45 watts. To draw 3.26 amps with 13.8 volts, you need a 4.23 ohm resistor.

Realistically, I'm going to guess that the computer would be OK if the actual current was a touch low, so I'd probably look for a five ohm, 50 watt resistor, and would wire it from the ground to the headlight "hot lead" on both sides. You'd probably get away with the same value for the high beam, if you're even going to worry about swapping it (not much advantage to an LED high beam - it's used very little, but could potentially be brighter).

And just now, I looked up these resistors, and see that the most common anti-bus error value is SIX ohms. Probably just fine, too.