Brake lights not working, third brake light works fine

Hi Guys,

I'm in a pickle and need some help. I"m going out of town tomorrow morning and I just noticed last night that my brake lights are out. Running lights, reverse lights, turn signals, hazards all work. The third brake light still works too. I've been searching on here and on other forums and I'm confused about how the brakes lights are wired. My rig is a 1999 XJ Sport, 4.0L. A few posts have mentioned that the brake lights run through the multi switch on the steering column. Does that include the third brake light? If so, then I can eliminate that as a possibility.

i'm assuming that since the third light works, my brake pedal switch is fine too correct?. I checked fuse #7 and the under hood fuse #23. (Again, if the third works, those shouldn't be the issue either right?)

I've swapped the bulbs and still no lights. Anything else I can try?

Thanks!

I'll check my 99 wiring diagrams later when I have time (have the FSM still) but I'm pretty sure all brake light wiring goes together, until it gets to a connector behind the spare tire, which is also the point where trailer wiring is taken off. The first thing I'd do is check the tail lights for a proper ground. A ground issue is almost certain if any other filaments light dimly when you put on the brake. If grounds are all right, I'd start checking continuity from the terminal behind the spare. As I say, I'm a bit rushed now, but I think the wiring passes from left taillight to right, so if signal is not getting to left, it will never get to right.

Matthew Currie said:

I'll check my 99 wiring diagrams later when I have time (have the FSM still) but I'm pretty sure all brake light wiring goes together, until it gets to a connector behind the spare tire, which is also the point where trailer wiring is taken off. The first thing I'd do is check the tail lights for a proper ground. A ground issue is almost certain if any other filaments light dimly when you put on the brake. If grounds are all right, I'd start checking continuity from the terminal behind the spare. As I say, I'm a bit rushed now, but I think the wiring passes from left taillight to right, so if signal is not getting to left, it will never get to right.

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im no expert... but i dont think itll be a ground. the turn and reverse also share the same ground. and the OP stated that those all work properly.

ive been wiring a set of trailer LEDs for mine, and had problems with a fuse under the hood, but i dont think it was number 23. i could be completely wrong, but i think it was somewhere between 13-20. ill have to check my FSM when im out of class....

do you have running lights, but just no brakes?

Looking at the wiring diagrams in the FSM hardly helps, because they are utterly confusing, and incomplete, and the connectors referred to are not shown in the connector illustrations either. However, from the best I can figure, if you're getting center brake light, the current is getting to the rear, and your problem is likely to lie somewhere between that and the taillights. It is unclear from the diagrams exactly what goes where, but it looks as if the line for the taillights breaks out from a connector in the header, and goes from there to the trailer connector and the taillights. It also appears that the lines go to each taillight separately, and not through the left first, though it's again hard to tell. I'd look for a signal at the connector behind the spare tire first, though.

edit to add: I realize that a ground fault is less likely when other lights work, but it is not impossible, because often with a bad ground, adjacent bulbs which share the bad ground may serve as an alternate ground and be lit in the process. Having both lights out makes it very unlikely, but without looking at which bulbs light when, it is not 100 percent certain that the right bulbs are lighting.

the brake light circuit does not go through the MFS

there is a splice that connects right, left and center circuits together. My diagram says it is near the power amp... wherever that is.

white/tan wire.

check your bulb sockets for power and ground with a test light first and work from there forward to the splice.

if there is a power amp it will be behind the right trim panel in the rear, near the right side tail lamp ground point.
The splice will be in that main harness that's there.

The stereo power amp is usually mounted underneath the rear seat.
There is a harness that transitions thru that area which may be what you are looking for....

CharlesS said:

The stereo power amp is usually mounted underneath the rear seat.
There is a harness that transitions thru that area which may be what you are looking for....

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Figures.

Goes to show that you can't even trust the 'professional' repair manuals because their info is flawed. I really wish I could get unadulterated, reliable factory info in the world of an independent repair shop

:dunno:.

I didn't see any reference to a power amp in the FSM - this is not to suggest that those saying it's there are wrong but to emphasize that the wiring diagrams are a mess. To trace any circuit one must jump among widely separated pages. It's not too bad if you are sitting in the car with an ohmmeter, but it's pretty near impossible to use as a reference otherwise. Nowhere in the book is a single diagram that shows an actual route for those wires.

At least it's better than the 95 diagrams, which while a little easier to follow, included wires that actually could not be found, or the 96, which reported the pinouts for the radio connector wrong (my son blew a new radio following the pinouts).

in Michell's ProDemand wire diagram, splice S302 for the brake light white/tan wire shows a note that the slice location is near the power amp.

in component locations splice S302 is said to be "near the power amp"

I did also find that component locations says the power amp is under the left side of the rear seat. (after I posted that I thought it was behind the tail light)

G403 which is the ground point for the right tail lamp is said to be " between the right tail lamp and the power amp" This is why I concluded that it was in the right rear corner. As it is, that's a lot of hidden wire harness to trace when the amp is under the left side of the rear seat.

f'n engineers.

Sorry it took so long to back to you guys. I just got back from my trip. I ended up figuring out the problem. It turns out it was a ground....At least I think it was. I looked again at the original bulbs and the new ones I put in. All of them had the 2nd filament burned out. I ended up pulling the interior where the spare is mounted and found that there was an exposed wire. After rewiring and making sure everything was nice and protected, I put new bulbs in. Presto...got brakes again. I'm guessing that exposed wire was somehow shorting and causing the brake filament to burn out. I have no idea why the other filament didn't burn out too, but that's probably becuase I'm no electrician! Thanks again for the responses everyone.