2000 Accord Coupe Brake Lights

[mrfixit]

Hi all,

I'm (obviously) new, but I've been reading here for sometime as I try to fix my 2000 Accord Coupe. I know this topic has been discussed before, but I've not been successful with any advice thus given. So here goes...

My problem: both left and right brake lights are out. The center (window) brake light works just fine. Every function of the tail lights work (signals, running lights, etc) except the brake lights. The do not light up under any circumstance.

My first Macgyver: I hot wired both left and right brake lights to the center brake light. (I cut the power supply wire from the side lights (black/white) and spliced them to the center light. It worked just fine, but is only meant to be temporary.

What I've tried with no success:

-I replaced the wiring harness for both tail lights in case of a bad socket and to fix my temporary solution.

-I replaced the Brake Light Failure Sensor (as others have suggested)

-I checked all fuses & relays

-I checked all grounds

-I checked all wires for shorts/breaks

-I replaced bulbs (as mentioned above)

Here is what's odd: I used a multimeter to do some investigation. I can detect 12v of power going into the Brake Light Failure Sensor. But there is no power coming out. I am not ready to believe that my new-from-the-dealer sensor is bad. Here's why: If it jump the Black/White power-in to the Green power-out, I cannot get any reading at all from the Black/White wire.

I am at a complete loss here. I feel like my car is defying the laws of the physical universe! I know some of this is probably not clear, and I will answer any questions as soon as possible. Thank you in advance for any answers and for even reading this diatribe.

 

[chaby_91]

What we know is that your brakelight bulbs aren't getting any power. This is what you should look into.

If somebody can post a wiring dragram, I would be happy to help.

 

[RedRyder]

The bulbs are getting power, but only on the dim leads (since the running lights work). So it must pertain to the wiring for the bright leads.

So the running lights in the center tail section are doing the same thing as well? Running lights work but not brake lights?

 

[mrfixit]

Hi,

I have the wiring diagrams at home, so I can post pics later this afternoon (after work). I will also indicate which wires have power and which do not. (I will make them as high quality as I can, but they're coming out of a manual via a cheap scanner and/or camera)

To answer the question, yes, running lights work, but Brake lights do not. The lights on the trunk door (not the window light) do not get brighter when brakes are engaged. ONLY the center window brake light lights up. From my understanding, it gets direct power from the brake light switch, so I know the switch is good.

Thanks for the replies so far. I'll get the diagrams up asap.

 

[chaby_91]

I have found this.

The 3rd brake light is the only one that's not going through the brake light failure sensor. Bypass the sensor, press on the brake pedal. Also look for corroded or loose connections, then report back.

 

[mrfixit]

Thanks for finding that image - saves me some time.

Based on the diagram shown:

I can measure 12v in the Brake Switch Input wire (black/white) going into the Brake Light Failure Sensor.

NO current is coming out the Brake Light Input wire (green) from the Brake Light Failure Sensor.

I have tested the green wire for shorts/breaks via Ohm meter and read 0 resistance. I will double check it tonight though.

I tried to bypass the BLFS but something odd happens. I'll try to explain: I jump the black/white wire to the green wire (in the plug that goes into the BLFS) using a normal insulated piece of wire. When I do this, I can't read any current on the wire. If I remove it from the green wire socket, I can measure 12v. So basically, as soon as I bypass the BLFS, the white/black Brake Switch Input wire goes dead.

Like I said, I'll double check the green wire, the bulb sockets (which are new from the dealer), and the grounds again tonight for continuity.

 

[chaby_91]

also check the yellow wire for 12v and the sensor's ground

 

[mrfixit]

Sorry for the late response - my home internet was down all night thanks to some genius with a backhoe.

Anyhow, I have the wiring diagrams, but I have no idea how to upload them.

I checked the following last night:

-Yellow wire (ignition input) out of the BLFS has 12v.

-Rechecked all grounds for continuity

-Checked green wire (brake light input) for continuity

Everything checks out. I checked to make sure sockets/plugs were conductive and couldn't find a problem. Also, for some reason, I can't bypass the BLFS. The system goes dead when I jump the Brake Switch Input (white/black) to the Brake Light Input (green).

This leads me to believe there's a short somewhere, but I cannot measure one. I've checked the green wire multiple times for continuity and it checks out at every brake light socket.

 

[chaby_91]

3rd brake light works. That means fuse is good, pedal switch is good and circuit good down to at least the split between 3rd BL and C554 to BLFS

Your testing of the grounds must be good

If there were a short, the fuse on that circuit would be blown. If not, wires would get very hot and possibly start smoking and your battery would die quickly.

but then, IDK how that sensor works. Here is what I'd do.

Unplug C554. There should be 12v at the power end when the pedal switch is pressed.

Unplug the BLFS. Test that bit of wire for continuity between both ends of it and with ground. That wire must be OK for the 3rd brake light to work...

At this poing, the sensor should be getting power through the wht/blk wire. Check that.

Unplug the green wire from the sensor and every bulb. You mentionned the wire was good. Test the wire for continuity with ground. There should be none, DVOM indicating O/L or MAX or something.

If you do get continuity between the open green wire circuit and ground, you do in fact have a short. Maybe the sensor prevents the fuse from blowing.

If the green wire is OK, try jumping it again from the WHT/BLK to GRN wire, with the pedal pressed. All bulbs should light up. This is a simple bypass of the BLFS and nothing on the wiring diagram indicates that this should not work.

if your continuity tests indicate high numbers, you may have a parasitic draw in your circuit that's taking all the power away.

Try that and report.

 

[mrfixit]

At this poing, the sensor should be getting power through the wht/blk wire. Check that.

If the green wire is OK, try jumping it again from the WHT/BLK to GRN wire, with the pedal pressed. All bulbs should light up. This is a simple bypass of the BLFS and nothing on the wiring diagram indicates that this should not work.

Try that and report.

Ok, I'll check for continuity between the green wire and grounds and make sure there isn't some problem going on there.

I have verified power in WHT/BLK that connects to BLFS. So I know it's not a connection issue at C554. However, I'll unplug/replug that just to make sure everything connects well, and I'll test its grounds.

I have jumped WHT/BLK to GRN and when I do that, the wire goes dead. This is what is perplexing me the most. That doesn't seem possible, but I swear it happens every time. I can 'plug' in a piece of wire to the WHT/BLK wire socket and measure 12v on that wire. As soon as I bend it and plug it into the GRN wire socket, voltage drops to 0. Maybe GRN is connected to a ground somehow? I don't know, but I'm sure the GRN wire is the culprit at this point. I'll test it for continuity with all other wires and report back though.

Thanks for your help so far!