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FIXED: Strange problem with brake light circuit - there must be a short somewhere!


Legendary Member
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Tech Expert
1 August 2008
City of Angels
During my long 2hr drive home from the track last night my "BRAKE" warning lamp on the dash cluster came on and started intermittently blinking. My Cruise Control was also disabled (it appears they're on the same circuit) when this fault appeared. I pulled over to the side of the road twice and after pulling back the rear carpet and inspecting the tail light sockets, plugs, and bulbs there was nothing that seemed out of place. It was dark, late, and driving back from the track leaves one traversing rather sketchy parts so I didn't really stick around if nothing obvious was out of place in the wiring. My rear trunk release switch (on the driver's door panel) also stopped working on the 2nd stop and didn't want to start/stop the car in case it wouldn't start again. The trunk switch started working again when I got home.

The prime suspect points me to my recent tail light swap. I swapped with another owner for his 02+ tail lights for my JDM "dark" tail lights. We did the swap "wholesale" per say which means I gave him the entire assembly and he took mine (i.e. taillight housings, bulbs & sockets, wire harnesses, brake lamp sensor, even the padding and trim pieces, etc. In retrospect his was in worse condition than what I gave him but this was simply due to age (more on this later). This is my first long night drive on them and first time using cruise control at night. I have driven the car a few times during the day since the tail light swap with no issues. This is why the likely suspect problem is occurring in the tail light assembly area logic would dictate. There is some mild corrosion on one of the brake light bulb and socket contacts but again nothing obvious.

Being that stop light circuit seems to have been working fine for perhaps approximately 100 miles, I'm leaning towards the circuit of the parking light itself.

Before I go through and tear apart the car trying to find the source a search seems to point me to 2 likely suspects.

* Problem with the guage cluster - unlikely because i'm using new components from @Johan@SjoebergDP but this thread seems to suggest the cluster was the problem http://www.nsxprime.com/forum/showthread.php/44239-Problems-with-my-Brake-Lamp-Failure-Sensor

* Problem with the brake lamp warning sensors - these suckers aren't exactly cheap so i'm following the bypass procedure outlined here as a diagnostic exercise. I have reason to believe these sensors are a least 15 to 20+yrs old but i'm also not sure if the 02+ used different sensors than the pre-02's. A parts search suggest they have the same part # http://www.nsxprime.com/forum/showt...arning-bypass-what-am-I-doing-wrong?p=2028607

I'll be going over all the fuses, scrubbing all the contact points, and go from there.

Perhaps one of our gurus can assist in pointing me the right way? @Old Guy? :)

This is a photo taken when I got home last night. This may seem brighter than it actually is. Don't let the Android photo deceive. It was several shades darker in real life. It's to a point where I could probably bare see the lights if I was following myself on the fwy. The bulbs are very dim as if there is a short circuit or a voltage back-feed somewhere in the circuit. The strange part is why are the signal bulbs illuminated and why is there current running to the 3rd brake light LED?

This is a photo with the brake pedal depressed. Notice full illumination in the 3rd brake light AND the turn signal lamps but nothing out of the main brake lamps. Do the brake light sensors have a circuit for the signal lamps as well?

Things get more strange when I turn the dashboard signal level left or right or even when the hazards come one. I didn't want to do that for any amount of time in case there really is a short somewhere.

Any places I should start looking? Thanks in advance!

EDIT: It just occured to me that I did a lot of work on the driver's side bucket seat rails. I hope I didn't pinch a wire harness below the carpet somewhere. I'm normally pretty good with this but I also like to sit on the side bolster for comfort. perhaps I could have pinched a wire there as well. Darn! I'll be checking this as well.
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It took longer to write this post than it took to find the culprit.

This grounding block was very loose. I have no idea how that got loose as I don't recall ever needing to use this as a grounding location for an accessory. I tightened it up with some light dielectric grease and all is well. Glad it was a simple fix.

I'll leave this thread up in hopes it will be useful for someone.

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Where is that grounding block? May help with other people that have the same issue.