My 91 Accord LX sedan shows the brake warning light on the dash.
I took a look at the bulbs--Left bulb lights up when brake pedal is pushed, right one does not.

I switched the bulbs to test them--both bulbs light up correctly in the left side, but not the right, so bulb is not the problem. Both bulbs look okay--both filaments (running and brake) intact and not burned out; both inserted correctly into the sockets.

Further testing: I turned on the running lights, and looked at the bulbs.
Left bulb: On at what appears to be full brightness.
Right bulb: On, but dim, about half the brightness (or less) of the left bulb!

Then with running lights on, I held the brake pedal down with a stick and looked at the bulbs again.
Left bulb: running light filament on, brake light filament on.
Right bulb: running light dim (as noted above), no brake filament on.

Okay, electrical gurus, what's next to check to fix the problem? I spent a while looking at the forum to see if somebody else has a fix for this, but I didn't find an answer (unless I missed it).

 

What is happening with the high-mount brake light?

The running light and brake light get voltage from different sources, so I would suspect the ground side of the circuit to be a problem.

You can quickly test both sides of the circuit. Do you have a volt meter?

 

The "failure sensor" often gets rust and that from a leaking tail light gasket.....and the right rear seems to be the worst for some reason.

 

High-mount brake light status: not operating when the brake is applied, but the bulb looks fine.

I do have a volt-meter--what's the process for testing the circuit?
I saw three wires going into the bulb socket--I guess one is ground, one is running light circuit, and the other is brake light circuit.

The sides of the bulbs do show very light discoloration/corrosion, but I can wipe it off with a cloth, so it's not severe. After wiping the bulbs, there doesn't appear to be any change.

 

I was looking at the wiring diagram on autozone.com. It isn't the greatest diagram, but it gives you an idea of the basic setup.

It looks like the failure sensor could be the problem with the high-mount and the right tail light. The wiring could be the issue too.

What are the wire colors going to the bulb that is not working properly?

 

Again, my two cents.......open the cover to the right/pass side tail light....wiggle the wires going into the brake light failure sensor while the brakes are pressed.....what happens?

 

Wiggling the wires doesn't seem to do anything that I can see.

 

I found my 91 Accord Shop Manual on PDF, with handy pages with the relevant wiring diagrams and troubleshooting guides. I'll link to them as JPGs on my own website, so you folks can see them. :
http://home.comcast.net/~lukeythetru...135_Page_1.jpg

http://home.comcast.net/~lukeythetru...135_Page_4.jpg
http://home.comcast.net/~lukeythetru...135_Page_5.jpg

Here are my actual wire colors, as they go into the bulbs:
LEFT
Running tail light: Green-Yellow, Black
Brake light: Green-White, Red-Black, Black
Turn signal bulb: Red-Black, Black

RIGHT
Run: Green-Yellow, Black
Brake: Green-White, Red-Black, Black
Turn: Red-Black, Black

And, of course, the colors in the shop manual are different indicating which wires as they go into the failure sensors (see page 16-135 in the shop manual)
LEFT
[Wht/Grn] [X] [X] [Grn]
[Grn/Wt] [ Grn/Wht] [Grn] [x]
Manual-->[Wht/Grn] [X] [X] [?]
Manual-->[?] [?] [?] [Grn]

RIGHT
[Grn/Wht] [x] [x] [grn]
[Grn/Rd] [Grn/Wht] [Blu/Grn] [Grn/Blk]
Manual-->[Grn] [x] [x] [Blk]
Manual-->[?][?][?][?]

I pulled off each failure sensor and opened it up. Both look clean inside--no corrosion, burns, dirt, etc. I checked continuity with my voltmeter, and the sensors seem to have good circuits. The LEFT one is different from the RIGHT: only two coils in the Left, plus the diode for the failure sensor. The RIGHT sensor has three coils--probably one for the high mount brake light.

So, I did the trouble shooting on page 16-135, to check the failure sensors, but I'm not positive of the test results, since the wire colors in the Sensor Test checklist DO NOT MATCH my actual wire colors. Thus, where the manual says (Left side, step 3) "...GRN terminal..." I have two GRN wires, so I tested them both. On the Right side, where the manual says "Make sure the [brake lamp] does not come on when the ignition switch is turned from OFF to ON with the GRN terminal of the 8p connector grounded...", I have a Grn/Wht wire where the manual says Grn. Also, I am not sure if I truly grounded the wires out correctly (I am not experienced with voltage testers and electrical circuitry).
However, if I did the tests right, I got as far as Step 4, 1st bullet ("If the [Brake Lamp] comes on...") This could means that my failure sensors are OK.

I took out my voltmeter, and tested for voltage.
Left Brake socket: 11.5 volts-->works fine
Right Brake socket: what seems to be 9 volts -->this one is not lighting up.

I also looked at my rear turn signal lights--the right one is NOT lighting up. I checked the bulb--it's fine (visual check of filaments intact, voltmeter shows intact filament with some resistance). So clearly power is not getting there, either.

The High Mount brake light is NOT lighting up. Voltage check on it is 0 volts. The bulb is new and fine, but no power is getting to it.

----
Okay, that's the information that I have so far. I believe that the black wire is Ground for all bulbs. I believe that the Grn/Wht wire is power to the brake lights, and the voltage test on my right socket shows that something is not right with the wires/sockets over there.

What should I do next, Honda people?

 

Oh, and another useful link, with a diagram and detailed techie explanation:
How an Accord's Brake Lamp Work.

Brake lamp failure sensor
How Honda Accord's Brake Lamp Work

 

Well, it looks like a bad wiring harness on the right hand brake light assembly. I was tracing power to the brake light, and I got 12 volts from the wiring coming from the Left side to the right side, then 12 volts up to the failure sensor, and zero volts to the brake lamp socket.
Puzzling--until I wiggled the wires the correct way. Then suddenly the brake lamp lit up. Wiggling the wires that plug into the failure sensor causes the brake lamp and the center high brake lamp to come on. So, clearly I have some dodgy wiring right there.
I have to wonder why Honda built this circuit in a SERIES, instead of PARALLEL. Oh well--I'm glad to have figured it out at last.