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The third brake light works when I start car then after 2 or 3 taps on the brake it quits working.

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    They are LED lights I think, and are probably expensive from the dealer. I'd try to find one from ebay or a junkyard and swap it out. – cory Dec 5 '16 at 21:06
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    Is the "2 or 3 taps" sitting in your driveway? Or when you're driving? – kyle_engineer Dec 5 '16 at 21:47
  • Kyle, it is about two or three taps of the brake. Once when I hit brake to change to reverse, another before I head out of driveway and last at first stop sign I come to. – Cindy Bryan Dec 6 '16 at 14:34
  • The voltage converter (LED lights need conversion to run off of automotive voltage) is probably heating up and opening an internal circuit or opening a PCB trace. The only easy solution is to replace it. – SteveRacer Dec 7 '16 at 1:43
  • ok, thank you Kyle – Cindy Bryan Dec 7 '16 at 17:29
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The internal voltage converter (LED lights need conversion to run off of automotive voltage) is probably heating up and opening an internal circuit or opening a PCB trace.

The only easy solution for this problem is to replace it.

A good verification test would be to press and hold the brakes after you start for a few minutes to see if it goes out. If it does, the electrical assembly in side is defective, probably overheating. If it stays on solid for 2 or 3 minutes, the problem is vibration induced, and electrical connections should be checked.

@cory is correct; if you need to replace it eBay or a junkyard will likely be the cheapest source.

  • Actually, the circuit is converting voltage to fixed current, not to fixed voltage. The voltage it is using may vary depending on the temperature of the LEDs. LEDs require a fixed current and whatever voltage this fixed current requires. – juhist Feb 5 '17 at 9:21
  • @juhist Yes, this is sort of true, but when we speak of CHMSL (aka 3rd brake light) we are not talking about a single diode. If any or all the matrix of diodes is wired in parallel, sometimes constant voltage is used across the matix to assure proper current, which would not be possible with constant current due to variations in individual diodes in the matrix. It varies by application. I should have said *automotive electricity" or "power", rather than "voltage". Diagnostically this is still the correct answer to the OP's question. – SteveRacer Feb 11 '17 at 3:03

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