hi all, first post here!
I have a 1990 Accord EX coupe. the LH brake light will not come on, all other lights work. here is what I've checked, any ideas?

-changed the bulb, didn't help.
-tried the socket from the RH side, same problem so it's not the socket or female side of the connector.
-ground is good
-tested the male side of the socket on LH side and it has power coming in.
-no fuses are blown.

I am stumped now, since the socket has power going to it, why wouldn't the brake light come on?

I thought it might be an issue with the brake light switch up at the brake pedal but the other two brake lights come on so that shouldn't be the problem. (I checked that though and it seems fine).

Is there some relay that could be faulty and somehow cause the one brake light to not come on? Maybe turn signal relay?

Thanks in advance for the help!

 

Humor me.....are you actually testing the voltage from the "bottom" contact inside the connector, where the base of the bulb would contact? Also verify the ground from the outside of the socket?

If voltage and ground are still there......what happens if you press (lightly) on the bulb into the socket....and or slightly twist it.

Of course all of this is with the brake pressed.

 

Thanks for the response. so I have tried plugging in the socket assembly from the right side onto the wiring harness connector from the left side and get the same result, so I don't think it is an issue with the sockets. I tested the voltage at the pin on the male side (wiring harness side) and it was at 11.5v (with brake pedal depressed).
also, the tail light bulb that is part of the LH socket assembly will light up, but the brake light bulb that is part of the same assembly will not (no matter if I use the assembly from the LH or RH side).

I do have an aftermarket alarm installed also. I know that alarm is wired to flash my brake lights when the alarm is going off, maybe there is something in the alarm causing the brake light to not light up?

 

At the bottom of the "socket" are two pins....one sends power when the lights are on, one sends power when the brake is pressed......Please verify both contacts.

Then, the "failure" sensor on the tail light could have gone bad. They are different from left to right so that is why I'm trying to figure out is the same "pig tail" from the right would/will be good test on the left.

SO, are you getting ~12v to the bottome pin of the socket when the brake is pressed?

 

Your car has both left outer brake/taillight and a left inner brake/taillight (just like the right has a right outer brake/taillight and a right inner brake/taillight). Are they both out on the left side?

• If you get a voltage reading at one of the sockets on the left side for the brakes; but, it still does not light up, it may be a ground issue on that socket.
• If one or both sockets on the left side has no voltage reading, it may be an issue with the wiring from left brake light sensor or faulty left brake light sensor.

The Orange wire on the left outer brake/taillight socket supplies power (+) and should have voltage when the brake pedal is pressed. The Grn/Red wire on the left inner brake/taillight supplies power (+) and should also have voltage when the brake pedal is pressed. The Red/Blk wires for both sockets are to supply power (+) to the taillights when the lights are on. Right now, focus on whether there is power (+) at the orange wire and the grn/red wire, as those are to light up the bulbs when the brake pedal is pressed.

(Grn/Red will also connect to a Grn/Blu wire at 8P gray connector (connector C716) and 4P gray connector (connector C710).

 

LH side wiring harness (male connection):
-green/blue wire: 10.5v
-red/black wire: 10.5v
-green/black wire: 0 volts.
(green/blue wire is brake light power. if harness has power why wouldn't brake light come on? ...again, I've tried three separate white plastic housing/bulb assys also, same thing on all three).

LH side wiring harness continuity:
-green/blue wire: 530 (definitely not zero).
-red/black wire: 0
-green/black wire: 0

RH side wiring harness:
-green/red wire: 10.5v
-red/black wire: 10.5v
-green/black wire: 0 volts

RH side continuity:
-green/red wire: 0
-red/black wire: 0
-green/black wire: 0

 

I'm thinking it is the failure sensor that has gone bad. where is that located on the car? wiring diagram shows a left and a right failure sensor, not sure where they are though...

 

Refer to my post #5 above.

Have you checked the green/red and the orange wires? Both the green/red and orange wires on the left side run through the same left brake light sensor. It may not be the brake light sensor if you get power at the grn/red and orange wire on the left side. If you get power at those wire, then it may be a ground issue. If you get no power at either of the green/red or orange wire on the left side, it may be the brake light sensor.

 

If you follow the orange wire, it will connect to the left brake light sensor.

 

Maybe pics will help? (See below).

--I don't see any "orange" wire on this harness. There is a red/black wire that should be power for the tail-light. My tail-lights come on though, it is just the one LH Brake light that does not (which is the green/blue wire).

--I noticed that the continuity on the offending green/blue wire is not zero but 530ohms, or 5.3...whatever, not zero anyway. ...So, maybe it is a ground issue? But, if that is the case that wire should not show 10.5v power, right?