Two rear brake lights are not working

Tiny
MOLONEYG
  • MEMBER
  • 2005 HYUNDAI TRAJET
  • 2.0L
  • 4 CYL
  • FWD
  • MANUAL
  • 150,000 MILES
Middle top center light is working. Brake light switch seems fine. Continuity is fine and power in is fine. Cannot find a wiring diagram. So what to check next? Bulbs are working, but I put in new ones anyway. So it is between the brake pedal switch and the bulbs I know. Any guidance appreciated. Thanks
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Friday, November 4th, 2016 AT 11:58 PM

7 Replies

Tiny
CARADIODOC
  • EXPERT
If the brake light bulb is the same one that is used for the rear turn signal, the signal switch is the best suspect. The clue is not whether or not the signals work, but if they do, that proves the rear bulbs and the wiring to them is good.

Check the hazard light switch too. If that is built into the signal switch assembly, current for the brake lights goes through that switch too. The center high-mount brake light is on a separate circuit not related to the signal switch.
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Saturday, November 5th, 2016 AT 12:09 AM
Tiny
MOLONEYG
  • MEMBER
Thanks for reply. Was about to add I am in Ireland Europe so I have read signals not connected to brakes here. Signals and hazard working. Could it be BCM which I know nothing about, but I am sure I can locate and change if needed. Thanks again.
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Saturday, November 5th, 2016 AT 12:29 AM
Tiny
CARADIODOC
  • EXPERT
It gets simper than that. If you have separate rear bulbs on the rear; one for brake light and a different one for turn signal, then the signal switch is not involved with the brake light circuit. Instead, all three brake lights, left, right, and center, are all tied together. All will normally be fed right from the brake light switch, so if one works, they all should work. When just two don't work, I'd start by looking in the back for the splice where the wire to the left and right light branch off.

It is also possible for a light to have a bad ground and make just that one dead while the others work okay. There's two problems with this thought. First, you'd have to have two bad grounds for two dead lights, unless they are tied together and share a ground, but each brake light and each turn signal bulb typically also have a separate tail light built in, and those share the same grounds. Bad grounds would be a good suspect if the tail lights were also dead.

I don't think a computer is involved with the brake lights, but the engineers are insane and have seen fit to involve computers in every other circuit where they are not needed. Before you replace a computer, check all the fuses inside and under the hood. On most cars today there is a fuse for every circuit, instead of how they used to group many circuits together in the past. Also, those fuses are very likely not labelled as "Brake light". It's common now to find designations that no one can clearly understand, like "AL3", and "Comp WSP". If you are lucky enough to find one or two blown fuses, my first question would be if you had tried connecting a trailer wiring harness.
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Sunday, November 6th, 2016 AT 7:34 PM
Tiny
MOLONEYG
  • MEMBER
Many thanks Cardiodoc. I will try for the splice. There is a hitch attached with tail board wiring. Hasn't been used for couple of years but the wires going to the tail board socket look bad, have been loose and are pushed in around the spare wheel. Could that be the problem?

I have found a 'Brake' fuse on drivers side fuse board and its good.
Car is in very good shape generally so I doubt if splice was ever under stress but I will go have a look.

Thanks again.
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Sunday, November 6th, 2016 AT 11:45 PM
Tiny
KEN
  • ADMIN
Please let us know what you find so it will help others.

Best, Ken
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Monday, November 7th, 2016 AT 9:44 AM
Tiny
MOLONEYG
  • MEMBER
Ken,
You asked me to post the outcome here. Well, unfortunately never got to the bottom of it. Now that the clutch is now also gone I probably never will. Probably headed for car heaven. Thanks for your help though again.
Gerry
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Thursday, February 16th, 2017 AT 6:18 AM
Tiny
KEN
  • ADMIN
Sorry to hear that. Please use 2CarPros anytime, we are here to help and tell a friend.

Best, Ken
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Sunday, February 19th, 2017 AT 2:36 PM

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