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Chasing an issue with no brake lights at all when the brake pedal is pressed on my '93. All other lights work good and this includes rear signals & rear park/night lights. Both fuses on the driver kick panel are fine (along with the others there & engine bay). Just no brake light when pressed
I have a new Oem brake pedal switch from the FS section thread here on the way and the rubber stopper is intact on the pedal still. I did buy a Autozone/Duralast FD brake switch today just to try out in the meantime. Still nothing when swapped out.
I've also visually checked the TNS relay & looked at the contacts for rust etc. , nothing. (Fun to get to on Greddy Vmount). I went ahead and swapped the TNS & Retra Relays (blue relays) with each other to test - Nothing.
i even did a battery disconnect and swapped rear bulbs with each other and another spare set. Car on & off as well to test brake lights. No dice
Brake lights should turn on whenever you press the brake pedal, regardless of whether the ignition is on. So, the green/white wire connected to the big plug should have ~12 volts at all times. It supplies power to the brake light switch directly from the battery through the 3 fuses. The solid green wire ultimately connects the switch to the brake light bulb filaments, the powertrain control module, the cruise control unit and the ABS control unit, each of which then connect to ground.
You can also check for continuity to ground by working back from the chassis to the brake light sockets and then to the green wire at the big plug.
No power to green / white wire on the big plug of brake pedal switch harness. Like you mentioned, regardless of ignition on / off.
Verified 12 V for stop & tail fuses (ignition off) so power gets to kick panel fuse box for those 2. Also made sure the 60 Amp BTN fuse was good ( via continuity, pulled) and it was seeing 12V as well coming into its slot.
Everything else works, turns / back up / park / interior / cluster and headlights. I'm not the greatest with electrical so seeing if there's anything I can check within my scope somewhat.
I also left the probe in the green / white plug and tried moving the brake switch harness around for any voltage feed back - nothing.
So, you have continuous 12V through the 120A and 60A fuses to the 20A stoplight fuse, but not at the green/white wire terminal of the big plug?
If so, the green/white wire in the harness that connects the 20A fuse to the big plug must be open at some point. Test the green/white wire for continuity between those 2 points with your meter to determine if it is bad. The wire could be broken, or the problem could be as simple as a faulty pin connection where the green/white wire enters the big plug.
Or, try using a known good piece of wire to jump the entire green/white wire. In other words, temporarily run a wire from the stoplight switch itself (where the green/white wire pin in the big plug connects) back to the downstream side of the 20A stoplight fuse to see if the brake lights work when you press the pedal.
Before reading your reply, I had the same thought of the issue potentially being between the 20A and the brake switch of no constant 12V via green/white wire. I will verify the 60 & 120A fuse / constant 12V, which should be good.
For continuity green / white wire test, I can probe the harness switch end of plug (will make sure terminal is secure) but where would the other probe get access on the other end ? The wire seems to travel up into the steering colum and then behind the 20V fuse of kick panel ?
For continuity green / white wire test, I can probe the harness switch end of plug (will make sure terminal is secure) but where would the other probe get access on the other end ? The wire seems to travel up into the steering colum and then behind the 20V fuse of kick panel ?
You remove the 20A fuse and access the other end of the green/white wire at the 20A fuse socket terminal, but I'm not sure which of the 20A fuse socket's terminals is connected to the green/white wire and which is connected to the battery through the 120A and 60A fuses.
So, first, remove the 20A fuse and test each of its socket terminals to see which one is the "Hot" 12V side of the fuse. Then, probe the other (non-hot) fuse socket terminal for continuity via the green/white wire with the green/white wire terminal of the big switch plug. Good luck.
Leading up to today's diagnosis, I was narrowing it down to the power supply from fuse to switch. I rechecked everything that I could from relay / fuses under the hood to the rear bulbs / wiring / contacts. All good there for peace of mind. So I went into it thinking it's got to be the power supply wire from kick panel to brake switch.
Green / white wire had continuity from kick panel to terminal of brake switch harness. HuH. I was expecting nothing & indicating a green/white wire break. 20A Fuse in, it had power at panel, still not on other end of wire. Strange, something is up. Pulled 20A fuse and it has continuity, obviously no visual break. I decided to slap in another 20A spare fuse and when I checked the panel & harness terminal, it registered 12V power ! Well then, solved.
The 20A fuse in there was faulty even though it showed continuity (pic below) from the start of all this & visually intact. Gained some valuable intel on electrical topic, far more rewarding.
A HUGE thanks to Dave & Retserof for chiming in. Much appreciated 👍🏼
07-06-22, 07:01 PM
