Introduction: Car Brake Light Repair (LED Conversion)

Picture of Car Brake Light Repair (LED Conversion)

Contrary to what I had previously believed, the miniature lights that form the centre brake light strip are often not LEDs, especially on older models. In this case, they are tiny incandescent bulbs that run off the car's 12v battery, and (for this car in particular) seem particularly prone to failure.

Unfortunately, second hand salvaged parts were incredibly difficult to track down, and the cost of a replacement strip was about £40 and was only available from Taiwan, unless you count the £100+ listings from national suppliers. If I'd managed to find the individual bulbs for sale it would likely have cost around the same as the entire assembly, so I turned to the surprisingly cheap and easy option of DIYing a replacement light array.

Depending on your regional driving highway laws, I advise that you check the legality of performing the following repair as it will affect the brightness of the brake strip and (If wired incorrectly) potentially the reliability. That said, centre brake strips are often not mandatory as they are not always present on all cars.

Step 1: Identifying the Bulbs

Picture of Identifying the Bulbs

Depending on the make and model of your car, you may be able to access the array from outside the car, or from within (In which case you may need some of the fabric panels removing to get at it). Once you have located it, there will usually be a pair of screws on either side holding it in place, as well as a power connector.

I removed the screws holding the brake strip in, took off the outer housing, then re-connected it to the inside of the car to perform some initial tests. I found that many of the bulbs were in fact still working, but due to corrosion of the brass inserts and steel bulb terminals, more than half were not making a reliable connection, and even re-inserting them several times only resulted in a somewhat temperamental fix.

At this stage it is also handy to take multimeter readings by having someone else press down on the brake pedal. Here you should find it draws upon the full 12v of the car's battery (Or close enough to 12v!) and also identify the polarity of the brass inserts: While the incandescent bulbs work in either orientation, LEDs will only work if current flows in the correct direction, and since the battery is a DC source you will need to see which side is positive and which is negative.

One final thing to consider is a problem often encountered when upgrading older cars from bulbs to LEDs. LEDs of the same intensity are far more efficient than their incandescent or halogen counterparts, and draw much less current for a given voltage. Most cars' internal computers can detect the current flow through the lights and report an error if it is not the expected value. Unfortunately, this error threshold is not usually zero, so even though current will pass through the LEDs, the car may mistake the lower current for a broken bulb. Luckily, cars do not usually check for the current draw through the centre brake strip, as this is considered non-essential. A quick test can be done to see if this is the case by disconnecting the brake strip and trying the brakes. If you do not see any warning light on the dashboard, you should be able to proceed with the replacement.

Step 2:

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The original array used 10 incandescent bulbs at a spacing of exactly 30mm from each other. For the replacement LED array I used a 60 led/m SMD 5630 strip which only cost $1.60 for a single metre. Although there was a cheaper option for $1.25, the variant used here has a waterproof coating which will be beneficial if there is any moisture build up inside.

Led strips come in a variety of diode types and densities. Since I was using a strip with approximately 17mm spacing, there was 18 within the length of the brake strip rather than 10. The 5630 chip type (5.6mm x 3.0mm) consumes roughly 5-6x more power than the more commonly seen 3528 SMD LEDs, which is something to take into account when considering how bright this will be, although it may be possible to remedy an overly bright LED strip using light diffusers or tinted plastic.

It took several attempts to find the best way to fix the strip to the housing. My first thought was to place it on top of the brass inserts, but the back of the housing would need to be carved out to account for the extra thickness, and the pegs that hold the two halves of the housing together pass directly through where the LED strip would be. I could have cut the strip either side of the pegs, but since they have to be cut in multiples of 3, I would have ended up with a larger gap in the middle, and due to the difference in hole spacing I would need to cut extra holes for the extra LEDs.

I briefly tried to thread the LED strip through a hole cut directly into the reflective cavity and using wire loops to hold the strip in place, but due to difficulty in threading it through, I simply cut a much larger groove and used a small amount of silicone sealant to hold the strip against the back.

Prior to this I had soldered on a short pair of wires to connect the LED strip to the brass inserts. They were single core copper wire procured from some scrap CAT5 ethernet cable, and while a single pair would be sufficient for the power of this short strip, I soldered on a second pair to the opposite end in parallel for redundancy and more even load distribution. These wires conveniently threaded back through the holes of the older bulbs.

Step 3: Testing

Picture of Testing

Before soldering the protruding wires to the brass inserts on the other half of the housing, use a 9-12v battery to test your wiring and the polarity of the LED strip, as well as get a feeling for the brightness, and add resistors in series if you need to lower the light intensity.

I sealed the holes I'd made using a smaller strip of foil tape stuck back to back with a larger piece, then laid over the opening to provide a reflective surface on the inside (Not that it is likely to make much of a difference due to the relatively narrow angle of the LEDs.

Step 4: Re-Attaching the Brake Strip

Picture of Re-Attaching the Brake Strip

After checking the polarity one final time, I soldered the protruding wires onto the brass inserts. It helps to have a high-powered soldering iron since the size of the brass strips causes them to dissipate heat quickly.

After soldering and screwing the two halves back together, all that's left to do is re-connect the brake strip to the car.

The new LED strip looks far better with a higher density of light points, and is a decent match for the intensity of the side brake lights.

One final benefit is that the LED strip has virtually no "warmup" time, and when the brake is pressed down, the LEDs noticeably illuminate faster than the main brake lights, albeit by only a fraction of a second. This should mean the reaction times of other drivers in response to braking should be marginally improved!

Comments

crazypj (author)2017-10-07

I think a couple of 'armchair mechanics' are way overthinking things. (British definition 'Jobsworth') A working light will ALWAYS be superior to a non-working light. As a kit for repairing , probably illegal if it doesn't conform to all specs. As a repair, it's fine if it doesn't conform to all specs, I don't think any police are allowed to dismantle vehicle to check for conformity (maybe in Japan or German TUV testing station?) I know in Britain, the vehicle inspections don't allow tester to dismantle things to check suitability. All in all, I think it's a real good Instructable, not only from safety point but also aesthetics, 'broken' high level lights just look bad when only a few places light up

Morgor (author)2017-09-25

Hello good idea but :

Output voltage from the vehicles can go from 9 V to 16 V, there are no overvoltage protection on the LED Strip and unfortunatly Third lamp stop to be homologated must respect a flux level + specific color wavelenght.

White LED through Red lense does not make real red light !

Anyway considering the price of the spare part, comparing to do the real part price from the factory (less than 5 $) YOU ARE RIGHT !

Shadow Of Intent (author)Morgor2017-09-25

I'm not entirely familiar with the inner workings of cars, and you're right that the output voltage can vary, particularly depending on the power being supplied by the alternator. While there is no voltage protection in the LED strip, they are relatively resistant to voltages exceeding the recommended 12v, so it seems unlikely they would fail from this, especially since some car models with LED strips also have no voltage regulation / protection.

The strip I used has red smds rather than white. The red housing should filter out most non-red wavelengths as it does for the incandescent bulbs, and since the LEDs are of a very similar wavelength to those permitted through the red plastic, the main uncertainty was one of the light intensity rather than the hue, but this ended up being within expectations. As far as I can tell, the only litereature regarding the rear brake strip is that it should not exceed the intensity of the rear fog light, which it also conforms to.

Morgor (author)Shadow Of Intent2017-09-26

Just for your information: In Europe we have some rules for the input voltage : Must be be regulated by the car or the product 13,5 V + 0,2 V if I remember well !
If not done by the car the board topology must be Linear instead of resistive.

This product has no real design added value for the mid range car, so car manufacturer ask their supplier to do a simple as possible, anyway there is always a S1G diod and a transient one.

But finaly your solution is perfectly acceptable for this kind of lamp.

Morgor (author)Morgor2017-09-25

last point, there are no capacitor in // of led to prevent them from glowing due to EMC perturbation !

JeffM15 (author)2017-09-25

Nice Retro Fit

Bryan Carlile (author)2017-09-24

Excellent tutorial. I found it very informative and easy to achieve. I look forward to using this technique in the future. Thank you.

ajayt7 (author)2017-09-24

Grand idea to use LEDs

heavyweather (author)2017-09-24

Much better.
Though I guess it could be a problem if the car isn't licensed with LEDs. Might not be a problem with break lights.

TomN13 (author)2017-09-24

Good job, looks alot better. Savings are big $$$$

maniacse (author)2017-09-24

I made this on one C-class Mercedes few years back, but I think I choose wrong type of LED strip - it last only 2 years or so and stop working. I do not see it afterwards, so I can not tell, what was wrong. I used waterproof high output LED strip. I hope you will be lucky and get better result. Fingers crossed!

dhallsten1 (author)2017-09-24

very good write-up. thanks for sharing

LarryB119 (author)2017-09-24

Thank you, i have an older Cadi and this is a great fix..

travis_marsh (author)2017-09-21

In my opinion, it is looking much better than the orignal one.

Thanks! Aside from the fact it is now illuminated across the full width of the brake strip, larger gaps between the older bulbs (Even when they all still worked) made it look like a poor quality piece of technology.

bhvm (author)2017-09-18

very best mod

gm280 (author)2017-09-17

Ingenuity is always refreshing to see. I love to seen alternate ideas to fix things. And I can honestly say, I would have fixed that using LEDs as well.

Anshu AR (author)2017-09-17

Nice mod!

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