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Using LED signal/brake lights on a pre-MBUSA W463

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AlanMcR
Posts: 1922

Using LED signal/brake lights on a pre-MBUSA W463

Post#1 » Mon Feb 16, 2015 12:26 pm

A while ago, returning from Baja, I sat at the border for >1 hour and melted the brake light housings. Not wanting this to happen to my new housings, I replaced the standard incandescent lights with LED replacements. The replacements are about the same brightness, but not as well focused towards the rear.

Overall I'd rate them as 80% as good as the originals. They definitely won't get hot enough to do damage. One definite plus is that the brake lights come on ~200ms faster, which equates to about one car length at 65mph.

Unfortunately, the change over isn't quite as simple as just replacing the bulbs.

Brake lights: The ECU monitors the brake line to see if you might be stepping on the brake. That circuit expects to see an incandescent bulb. If you replace all three brake lights your engine will buck and flatspot like you just ran out of fuel. Many of the LED vendors offer "no error" versions that fix the problems for more modern vehicles. These didn't help. What needs to be done is to attach a small incandescent bulb into the circuit. A dash bulb will work, even a 24v bulb will work (it won't light up and it will last forever). I tucked the bulb into the center brake light in the back door.

BrakeLightsLED.JPG


Turn signals: If you want to go further and replace the turn signals, you'll find the same sort of problem. Replacing even one bulb will get you "hyper flash", where the turn signals will flash at double speed. The "no error" LED versions might fix this. Given that I had the LEDs already in hand, I decided to replace the flasher relay. Unfortunately, no one makes a LED-ready version of the W463 flasher relay. So, here is how to fix your own:
Open the flasher relay. Unsolder the current sense resistor (0.02 ohm) and replace with a 0.06 ohm resistor. The modified relay will work both LED and incandescent bulbs in any combination. Tape the old resistor onto the relay just in case you want to go back. Side benefit: your turn signal switch will last forever.

BlinkerFixLED.jpg

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vadimivanovich
Posts: 4593

Re: Using LED signal/brake lights on a pre-MBUSA W463

Post#2 » Mon Feb 16, 2015 12:32 pm

Right on Alan! My kind of hack :)

RussK
Posts: 58

Re: Using LED signal/brake lights on a pre-MBUSA W463

Post#3 » Wed Feb 18, 2015 5:36 am

I seen a few cars do the same thing, mostly because of stop and go traffic. Our fix was to drill a hole in the top of the lens, a couple small holes in the bottom, so cold air could rise into the lens and the heated air from the bulb would rise out of the top. We then took a piece of a air filter and glued it to the larger hole on top to keep out dust.
We don't see that as much now, but when plastic lenses became the norm it happened often here in the hot summers.
RussK

Gwanabe
Posts: 296

Re: Using LED signal/brake lights on a pre-MBUSA W463

Post#4 » Sun Apr 05, 2015 8:36 pm

Can you please tell us how you came up with 0.06 ohm resistor value? Thanks for sharing this with us.

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AlanMcR
Posts: 1922

Re: Using LED signal/brake lights on a pre-MBUSA W463

Post#5 » Sun Apr 05, 2015 9:13 pm

Gwanabe wrote:Can you please tell us how you came up with 0.06 ohm resistor value? Thanks for sharing this with us.

The sense resistor measures the current by building up a proportional voltage:
V = I * R
A working system needs to produce about the same voltage, otherwise the blinker goes into hyperflash to warn you of a dead bulb.
The LEDs draw about 1/4th of the current (I) So, to keep V in the same ballpark, R needs to go up by a factor of four. I decided to be conservative and only go up a factor of three. That turns out to work for any combination of LED or incandescent bulbs.
Measuring 0.02 (or 0.06) ohms is not that easy, the test leads for your multimeter will have more resistance than what you are trying to test A special 4-wire (Kelvin) test cable is what is normally used to get around that problem.

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G500Pur
Posts: 801

Re: Using LED signal/brake lights on a pre-MBUSA W463

Post#6 » Mon Apr 06, 2015 2:36 pm

Hi Alan, if I replace both tail light bulbs with LED, but leave the 3rd light in the rear window as stock, will that prevent an error code?

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AlanMcR
Posts: 1922

Re: Using LED signal/brake lights on a pre-MBUSA W463

Post#7 » Mon Apr 06, 2015 2:51 pm

That works, or at least it did on my 1996. All it takes is one incandescent. You can replace the center bulb too, just at long as you add a hidden incandescent somewhere.

Mcfly
Posts: 115

Re: Using LED signal/brake lights on a pre-MBUSA W463

Post#8 » Tue May 09, 2017 7:21 am

I swapped my markers/turns and rears with all LED, superbrightled.com
Also have Truck Lite LED headlights. Swapped my flasher relay for a Landrover style LED OK version...its what was in the shop at the time.

My issue is this:

Rear LED tail lights stay on at times. Sometimes only the left, sometimes both. Turn signal LED is brighter on the left rear compared to the right rear.

Any thoughts? Do I need resistors?

Marty

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