Converting to LED bulbs

Canadian Moose · Post by **Canadian Moose** » 28 Nov 2016, 20:22

I am in the process of converting my 2002 V70 to LED bulbs. I already have HID projector headlights so LED everything else was the next thing to upgrade. Tonight I swapped the brake lights, one set of the tail light bulbs and license plate lights to LEDs. Tail lights work fine, no issues. Brake lights however are displaying a warning message on the cluster about bulb being out. Looks like I will have to mess around with current sensing shunt or add load resistors. No biggie.

Just curious as to what I should expect when I swap front and rear turn signals to LEDs? Will they hyper flash or will I simply get a warning message? What controls the flashing? Is there a lightning control module or sorts like a on some Fords that has a built in flasher or is there just a flasher relay like older cars? Would someone have a wiring diagram for the turn signals so I could plan ahead?

s10lowrider1994 · Post by **s10lowrider1994** » 28 Nov 2016, 23:38

I had to use a load equalizer thing on my bike to make them work correctly. Didn't cost much and was easy to wire up, I imagine you'll need something similar to avoid the quick flashing and bulb out warnings.

Canadian Moose · Post by **Canadian Moose** » 01 Dec 2016, 19:48

I think I figured out how to disable the warnings by modding the shunts. Will post details when I swap all the lights to LED and verify they work.

Canadian Moose · Post by **Canadian Moose** » 13 Dec 2016, 21:07

After screwing around with this for the last week I came up with a solution. I tried using load resistors initially and and they got so hot within a minute of having the lights on that I just wasn't comfortable having them in the car because eventually they would start melting things or worse, start a fire. Plus using load resistors kinda defeats the power savings of LEDs.

The solution turned out to be quite simple. It involves modifying the shunts and replacing a resistor with one that has higher resistance thus fooling the REM into thinking the bulbs are still present. This is essentially what load resistors do except this is done at the REM rather than the bulbs themselves.

I got the idea from this site.
http://www.xenonvalot.com/xenonfixvolvo.html

I went to a junkyard and grabbed a bunch of shunts to mess around with. After inspecting the wiring diagrams I came to a conclusion that the shunt has a couple of resistors inside that are used by REM to sense when the bulb is out.

The resistance values listed on that site appear to be incorrect though. My measurements showed about 2.6 ohms between pins 2 and 3 as well as 1 and 2.

Here is a picture showing what a shunt looks like inside as well as a modified shunt.

Top left shows what a shunt looks like on the inside. I took a grinder to it and removed top layer of the plastic that exposed the guts. The metal traces that you see there actually act as resistors.

In order to modify it one of the metal traces needs to be broken and a new resistor soldered in its place. I ended up simple drilling a hole through the metal trace. Then using a box cutter I removed plastic covering the traces so I could solder a new resistor in its place.

I soldered a 10 ohm resistor in there to try. My theory is that once the resistance is above a certain value, the REM assumes that the bulb is not burned out.

So far I tried this on brake lights and tail lights and this eliminated the warning messages. Next I will be trying this on the turn signals.

volvodriver1 · Post by **volvodriver1** » 22 Oct 2020, 19:23

Hey Moose!

I read in another post that you were NOT able to get this to work for converting turn signals to LEDS.
I know its been a while but would you mind trying to remember what you tried and discovered?

Post by **darrylrobert** » 22 Oct 2020, 20:03

i used this guys but fine tuned it by using very small resistors to allow the bulb out feature to remain working. I also was not able to get the turn signals to work using this method, i did experiment with a variable resistor and could pinpoint the exact spot that triggered the fast flashing/normal flash but found this changes with heat making it very difficult. Ive ended up using LEDs on the back with built-in resistors, they were too bright for me so i partially covered them with a alumiuim tube (been working well for 12months)

Ive had to modify (add resistance) to nearly all my LEDS except the expensive Osram ones, they are all too bright.

volvodriver1 · Post by **volvodriver1** » 23 Oct 2020, 12:51

darrylrobert wrote: ↑22 Oct 2020, 20:03 i used this guys but fine tuned it by using very small resistors to allow the bulb out feature to remain working. I also was not able to get the turn signals to work using this method, i did experiment with a variable resistor and could pinpoint the exact spot that triggered the fast flashing/normal flash but found this changes with heat making it very difficult. Ive ended up using LEDs on the back with built-in resistors, they were too bright for me so i partially covered them with a alumiuim tube (been working well for 12months)

Ive had to modify (add resistance) to nearly all my LEDS except the expensive Osram ones, they are all too bright.

Im actually also trying to do the same with my headlights but I installed a wiring harness to power them and that's really messing me up. The harness (with built in relays and in-line fuses) supplies the power to HIDs directly and only uses the factory headlight sockets to power the relay. I think this means that proper resistance readings within the CEM's parameters via the shunts won't even be possible. I was told that measuring in the milliohm range takes specialized equipment so its a matter of trial and error if I want to get this to work.

I dabbled a little but by severing the bridge between leads 2 &3 and soldering a resistor into place but the resistors I had laying around wasn't built to dissipate the amount of heat it was giving off so the resistors went up in smoke. I'll try to get my hands on some wire-wound resistors and give it another try.

@darrylrobert What value resistors were you using in your experiments?

Post by **darrylrobert** » 23 Oct 2020, 21:18

I havent converted my headlights, yes a multimeter wont measure that small a resistance

For the shunt resistance, which i believe is what you need to modify ive heard that the resistor to use on the shunt is very small, i would try 0ohms to 0.5ohms, i also experimented with long lengths of different type of wire. im using resistors of 0.5ohms 1/4watt on each side of the shunt for parkers and brake LEDs, the more resistors you add in parallel the smaller the resistance becomes.

adding small resistors to the shunt creates zero heat because its inline, where as adding resistance across pos/neg (load resistor) creates heat

Post by **ndphotonl** » 06 Nov 2020, 05:47

For the headlights, you only need to to the drilling modification for the shunt in the front. I have been running LEDs in projectors for quite some time (on my S80). Highly recommended btw.

Volvo S80 2.4T Retrofit Projector by Andy Ramdin, on Flickr

Volvo S80 2.4T OEM US Lights by Andy Ramdin, on Flickr

interace2 · Post by **interace2** » 01 Feb 2025, 09:27

Can anyone please help with this drilling Mod? how does it work?
Are you supposed to drill thru and sever the metal trace in the shunt or just put a small hole in it?