Fixing a Ford Thunderbird Taillight

My brother-in-law loves American cars. So he has several, amongst them a 1998 Ford Thunderbird. Now this is a nice vehicle, albeit built the American Way, that is, to not last. So to his annoyance the LED taillights failed, as they seem to do, so instead of a nice red glow all along the rear there were five ugly black spots. Of course, replacement units (manual sez: do not repair, replace whole unit) either can't be bought at all or for astronomical prices.

So I offered to fix them, even I'm an avid cyclist myself. This proved to be quite a challenge. These units really aren't meant to be repaired! Eventually, attacked with a hacksaw we got to the innards, an HP module. It contains 4 times five LEDs in series, which means that if one LED fails the whole string goes dark, causing the ugly dark bands in the taillight. The failure of a LED is caused by mechanical stress (the trunk slams shut pretty violently, could be the cause) so I decided that all LEDs would have to be replaced.

Now these HP LEDs are more than 10 years old, and this particular form factor with three legs is nowhere to be found. I had tried 5 mm "straw hat" LEDs but they didn't fit. A similar type called hyperflux, with four legs instead of three, is very common however (got mine here) so I used that. I cut off one leg and the standoffs on the opposite legs. The fourth leg was bent to it would fit the board.

Eventually I had the whole PCB populated. Putting it together again and comparing it with the other unit I had in for repair showed that the new LEDs were much brighter than the old ones. They also drew much less current, about half (0.2 A @ 13.8 V). Replacing the 33 ohm resistors with 56 ohm 0.25 watt ones fixed that.

As I had carefully popped open the module by cutting off the plastic blobs I had to find a way to close it up again. By drilling the plastic studs (2.0 mm drill) and screwing it shut with #4 1/4" Pozidriv self-tapping screws (Pozidriv to annoy the Americans) it came back together beautifully. Finally I tested the two units and declared them fit to go back to their owner.

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