I had my car serviced yesterday at the dealer - a number of minor issues were reported

  1. Wipers are smearing - mainly due to road dirt as I had only recently replaced them
  2. Water ingress in tail light - its an LED Sealed unit so not a lot I can do about that
  3. Dim LED high level brake light.

My understanding is that LEDs are an all or nothing type of shot - so the circuitry itself must be ok, and rather it must be a low power (i.e. poor connection) issue.

Unfortunately I haven't had a chance to look at it in daylight so wont be able to confirm, but could there be other reasons for a brake light (specifically LED) to appear dimmer than it should?

Car is a late 2013 SEAT Leon.

1 Answer 1


LEDs are not all or nothing, your typical LED car light has several LEDs in it, so you can have partial failures if one or more go bad. LEDs last a very long time, however they do break early sometimes, and the circuitry is not bulletproof either, so you could have a partial failure of the unit.

The failure modes that would make sense are:

  1. Some LEDs have failed: this is unlikely, one I could see, more than one would be unusual
  2. LED block failure: On the LED lights I've seen the LEDs are not all on the same driver, they are usually separated in different blocks that run in parallel electrically. A failure of one of the blocks would take out all the lights on that block
  3. Insufficient power: if the regulator which supplies power to the unit is sagging, that is not supplying enough power I could see the lights being dim

My money would be on #2, however #3 is easy enough to test, just disconnect the wiring harness and use a multimeter to check the voltage.

  • I've done some digging - apparently theres a diode before the power splits to the three blocks of LEDs and it can go bad, I'll confirm early next week.
    – Mauro
    Oct 13, 2017 at 13:57
  • Sounds about right. You may or may not be able to fix it, these days circuit boards can be very tricky to work on, requiring more than a soldering iron and some desoldering equipment, however it may be worth a shot if the part is expensive to replace.
    – GdD
    Oct 13, 2017 at 14:03

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