We have an 08 Tahoe and when the third brake light was not lighting, I checked the fuse on the left side or drivers side by opening the drivers door snapped the plastic cover and looked for the third brake light fuse. After I replaced it, it worked fine. The fuse leads were dark but the fuse had not blown. Still replaced it and its been working for 3 years now without issues.
Third brake light not working
- Thread starter Chibluz
- Start date
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Okay. I got a rental FSM from alldatadyi.com. I Measured the input and output of the new brake lamp switch. I measured the voltage at the Brake Lamp Switch with the car running. The Blue/ White stripe wire Pin A Cruise/ETC/TCC Brake Signal had no voltage(open) till the brake peddle was pressed. 14.4 volts when pressed(closed). Pin B Pink Ingnition Voltage and the Pin C Orange/ White stripe have 14.4 volts with the pedal pressed and not pressed. Pin D Purple wire Brake Pedal Switch (closed) had no voltage till the brake peddle was pressed (open), 14.4 volts when pressed.
I'm trying to trace the Blue/WH wire from the Stop Brake Switch to the Body Control Module X5 Pin 6 and then out to the Center High Mounted Stop Lamp (CHMSL). It looks like it goes through Pin 5 of BCM X5 to the Auxilliary BCM X1 Pin B2 (XBCM) <Junction Block left I/P ?>. The trailer lights seem to get their power from this blue/whitr wire. I do have brake lights left and right at the trailer lights connection box.
I will try to trace the voltage into the BCM and to the XBCM X1 today. If I have trailer lights should my voltage loss be in my XBCM X1 area?
Do I have this correct so far? Any suggestions/ corrections are welcome!
Thanks,
Chibluz
I'm trying to trace the Blue/WH wire from the Stop Brake Switch to the Body Control Module X5 Pin 6 and then out to the Center High Mounted Stop Lamp (CHMSL). It looks like it goes through Pin 5 of BCM X5 to the Auxilliary BCM X1 Pin B2 (XBCM) <Junction Block left I/P ?>. The trailer lights seem to get their power from this blue/whitr wire. I do have brake lights left and right at the trailer lights connection box.
I will try to trace the voltage into the BCM and to the XBCM X1 today. If I have trailer lights should my voltage loss be in my XBCM X1 area?
Do I have this correct so far? Any suggestions/ corrections are welcome!
Thanks,
Chibluz
01Konvict
Boats n Hoes
You found the blue/white wire from the third brake (CHMSL) goes from BCM x5 Pin 6 and did it have voltage on it? I'm not 100% sure where the BCM gets its signal to turn on the third brake but you can always run a jumper between brake taillight wire and third brake to make it work. I did this to mine when I added the modded caddy third. I've since gone back and ran a dedicated relay to the third with signal wire from the CHMSL blue/white wire.
Mine had an issue with the LEDs in the light causing too much resistance which killed the output signal. I would disconnect the third brake light plug and volts would show back up then when plugged in it would quit again. Have you tried disconnecting the light and measuring voltage at the plug?
Mine had an issue with the LEDs in the light causing too much resistance which killed the output signal. I would disconnect the third brake light plug and volts would show back up then when plugged in it would quit again. Have you tried disconnecting the light and measuring voltage at the plug?
01Konvict: Yes, I had 14.4 volts at BCM X5 Pin 6 from the Brake Lamp Switch.
I found the auxiliary BCM - XBCM X1. I measured the pin B2 and it had no power. I will try to jump the the BCM output to the XBCM X1 input to see if the CMHSL works.
To answer your question I measured .4 volts at the plug in the top of the tailgate that goes to the CMHSL. If all else fails I will jump the brake light to the CMHSL.
Too be continued...
Thanks,
Chibluz
I found the auxiliary BCM - XBCM X1. I measured the pin B2 and it had no power. I will try to jump the the BCM output to the XBCM X1 input to see if the CMHSL works.
To answer your question I measured .4 volts at the plug in the top of the tailgate that goes to the CMHSL. If all else fails I will jump the brake light to the CMHSL.
Too be continued...
Thanks,
Chibluz
01Konvict
Boats n Hoes
Ok so you had volts on the only wire going directly to the third brake light. I would measure voltage on the blue wire at light with meter to ground on car not on plug. If still seeing .4 volts then try continuity on wire between front at BCM to rear at light. My thoughts are either a bad ground from plug to body or broken wire between BCM and plug.
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