Introduction: 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
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.
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
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
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!