Brake Light Issue

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JJS_JJK
Posts: 2
Joined: Mon Mar 29, 2021 3:46 pm
Car: 2004 Infiniti G35 Sedan

Brake Light Issue

Postby JJS_JJK » Tue Mar 30, 2021 2:06 pm

I ran into an issue where my brake lights stay consistently on and will only turn off when I disconnect the negative battery cable. I have already checked the brake switch and that is not the issue. There was a previous issue where it looks like the wiring for the wing light was wired into the interior reverse light. That caused an issue where the brake light fuse on the interior of the vehicle was consistently blowing. Before I owned the car the mechanic it was taken to tried to place a 20 amp fuse in the brake light fuse slot instead of the 10 amp. This caused the two wires connecting the reverse light to get really hot and burn off the insulation on them. I have since fixed that issue by tracing the wires back to where they did not melt and replace the wires. If I try to hook up the wing light to the same wires even after the issue was corrected, I still blow the fuse. I also ran into the issue where now my brake lights just stay on I did go under the steering wheel and I noticed when I would jiggle the brake light switch wires I would here some sort of clicking sound. I have tested all other fuses under the hood and dash and no other fuses are bad. I have not tried a draw test yet but was hoping someone may have ran into a similar issue and can lead me to the right direction. I took it to the Infiniti dealership and the spent a half hour telling me that I need a new body harness but they are not being manufactured for a 2004 g35 sedan. They also quoted me over 5,000 dollars and 40 hours to try and locate the issue.


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VStar650CL
Posts: 1419
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

Re: Brake Light Issue

Postby VStar650CL » Tue Mar 30, 2021 3:21 pm

Brake lamps aren't rocket science and you could rewire the entire circuit in a lot less than 40 hours. Aside from being LED's, the brake circuit on your G35 is more straightforward than most. There are 7 components, the Fuse Box, the Pedal Switch, the Shift Lock Solenoid, the ABS Controller, and 3 Brake Lamps. The problem has to be power where power shouldn't be, so you need to narrow the candidates as to where it's coming from. I don't know what you used to check the pedal switch, but the right tool is a test lamp. With the connector loose, you should have battery power on one side and no power on the other.

If you get power on only one side, there's a problem with the switch even if it looks okay. That can be either an electrical or mechanical issue, so first make sure you don't just have a missing actuator button or some silly misadjustment. If it looks okay mechanically, use the test light on the cold-side wire while manually working the switch. If the switch is bottomed and you still have juice on the cold side, the switch is shorted internally.

If you get power on both sides then there's a short to 12V someplace downstream. Leave the brake switch unhooked and start disconnecting the remaining 5 candidates one at a time. Start with the lamps, they're LED and it isn't unknown for the control boards to fail short. There's also a diode on the shift-lock circuit that could melt short and allow the lamps to be back-powered through the shift lock solenoid coil. Check the cold-side wire at the switch each time you disconnect something, if the light goes out then you found your culprit. If there's still power on the cold side with all 5 disconnected, then there's a short in the wiring. In that case I'd suggest simply re-wiring the whole bus, cut the PNK/BLU brake wire at all 6 places and run new wires from the brake switch to each of the other 5. Doing it neatly will take some time, but it won't be 40 hours!

JJS_JJK
Posts: 2
Joined: Mon Mar 29, 2021 3:46 pm
Car: 2004 Infiniti G35 Sedan

Re: Brake Light Issue

Postby JJS_JJK » Tue Mar 30, 2021 3:28 pm

Thank you for the information I will try all these this weekend when I have free time. How I tested the brake light switch was just simply unplug it and the brake lights remained on which is also what the dealership told me they did as well.

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VStar650CL
Posts: 1419
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

Re: Brake Light Issue

Postby VStar650CL » Tue Mar 30, 2021 4:24 pm

Nope, that doesn't tell you much. If they're on constantly, taking the switch loose mechanically tells you nothing, the lights would be on anyway with nothing pressing the actuator. You need to take it loose and press the actuator to bottom, then if the lights go out the switch is working. If they don't then it's a shorted switch or something else, so pop the connector loose from the switch and see if they're still on. If so, you definitely have a downstream short.. If the lights do go out with the actuator bottomed, the switch may just be misadjusted or you may have a missing actuator-stop on the brake pedal frame.


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