Brake lights will not come on

Tiny
SCOT91
  • MEMBER
  • 2004 DODGE RAM
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 180,000 MILES
When I turn my head lights on my brake lights will not work. When I turn the head lights off they work. Now all of a sudden the drivers side tail light wont even come on. I have replaced the bulbs, both circuit boards on the tail lights also checked all the fuses. I cannot seem to find the problem.
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Wednesday, July 12th, 2017 AT 4:04 PM

5 Replies

Tiny
CARADIODOC
  • EXPERT
Your first two sentences are the classic symptom of a broken ground wire. Start with a visual inspection of those wires. If we need to go further, do you know how to use a digital voltmeter?
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Wednesday, July 12th, 2017 AT 9:56 PM
Tiny
STEVE W.
  • EXPERT
First thing to check is if you are getting power to the rear tail light. Pull it open and with the lights on check for power at pin one (white/yellow stripe wire) in the connector. If you have power check the connector inside to see if the actual connector is loose on the pin on the circuit board.
Since all of those lights share a ground it is likely to be a power feed issue. From the park lamp relay. If it is turning on (should be if all the other park/tail lights work) then it is in the wiring to the left tail light, either the pin is loose or the wire is bad.

Now for the brake lights, the only common items between the headlights and the brake lights (if nobody has played with the wiring) are the forward control module and the IPM.

To see if it may be the problem, check at the brake light switch for power on one terminal and not the other. Then turn on the lights. If the power goes away now it is the IPM or forward control module,
Below are the wiring schematics to give you the wire colors to test.
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Wednesday, July 12th, 2017 AT 10:18 PM
Tiny
SCOT91
  • MEMBER
I do have a voltmeter but im not familiar On using them. I do have a test light. But I took my test light and checked the pins on the connector on the tail light on the side it isnt working. The only thing isnt making my test light come on is the brake light. I had the key on the off position and tried the 4 way blinkers and they wouldnt work. Only way they would come on is if I turned the key to the on position. And what is the IPM?
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Friday, July 14th, 2017 AT 1:44 PM
Tiny
SCOT91
  • MEMBER
Ok on the side that wasnt working its working now I wiggled the connector and they started to work. On the passenger side taillight the middle bulb is bright and the top bulb is kinda dull. The drivers side looks normal. What would cause that? But I have no Brake lights now even when the lights are off.
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Friday, July 14th, 2017 AT 2:24 PM
Tiny
STEVE W.
  • EXPERT
Here is a guide on the meter.
https://www.2carpros.com/articles/how-to-use-a-voltmeter

IPM is the integrated power module. Basically the fuse box and it's controls.

Wiggling the connector tells me you have either a weak connector pin or the wire is broken inside the connector. Both cause the same symptom. I would get a replacement pigtail and install it. That would repair both failure types at once.

4 ways not having power unless the key is on suggests the you may have an issue in the IPM, possibly a blown fuse or bad fuse connector.

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Friday, July 14th, 2017 AT 9:34 PM

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