996 rear lights

Hi, I've got a friend who's 911 (2000 996) rear brake and lid lights stay on when driving the car. The rear lights shut off when the car is turned off. I don't think it's the brake switch since it turns off once the car is not running. I tried to look at the brake switch but it was blocked by a cheese holed plastic box. I'd assume the heater box. Idk. While unplugging the lights we then came across an issue where the turn DS rear signal would stay on if the lights were on but would turn off if the lights were off. The issue went away after I replugged the lid light. I checked the fuses. All were good! Any ideas? Thanks

Bad ground

Any ideas of where to look?

Quotes source post: 15391456

Start at the brake light switch! As with most Euro cars, the brake light switch is ONLY powered when the key is on. Meaning, when the car is working correctly, if you were to apply the brakes with the ignition in the off position the lights will NOT come one. It is highly likely that your brake light switch is stuck in the on position (shorted internally) which causes the brake lights to be on while the key is on.

Thanks.

Hello. Quick question. Which of the two pictures is the brake switch? The switch we bought matches the clutch switch. I unhooked the red switch from the clutch area and the car still started. I'm bit confused here. Any guidance is much appreciated. I've added two more pictures. Displays the two switches from clutch area together and the part number we had ordered.

by the wiring diagram it should be the switch that has a solid black wire and an black with a orange line wire. So by your picture ita the black switch and not the red one.

Thank you. Please see attached picture. Then is this the switch? Why is it different? It's a friends car, so I'll need to look at it again but if the switch is the one below we might have the wrong part. I noticed on eBay they showed two different switch parts for the rear brakes lights. The two parts I was comparing was the new switch and clutch / cruise control switch I'm finding out. I've attached another switch which is also supposedly a brake switch. It look very similar to what would but up to the car. I watched a video online which was all wrong

OK here is what I found. I believe the part you purchased is correct but you removed the wrong one from the car. From what I show the correct part number for the brake light switch is 99661311302. The correct switch to remove from the car is the last switch that you showed in your pictures with the black and black/orange wire. You could check the old switch with a multi meter prior to removal to confirm it is the issue. With the key on the Black wire should have battery voltage (roughly 12 volts) assuming the brake pedal is not applied, the black/orange wire should NOT have any voltage. If it does than the switch is most likely bad (it could be a short to voltage in the wire harness but that's doubtful). The black/orange wire should only have power in the event the brake pedal is depressed. For some reason I cannot located the clutch switch in my wiring diagrams. I can only assume the differences in the two switch's is that the stop light switch is normally open - meaning depressing the brake pedal closes the circuit which applies voltage. The clutch switch may possible be just the opposite and it I normally closed and the circuit gets broken when the clutch is applied. Again this is only a guess since I cannot see a diagram of the circuit.

100% confirmed it for you now. I found another diagram of the cruise control. The red switch you showed on the clutch pedal is ONLY for cruise control cancel. The diagram agrees with your picture of the red switch and indicates the wire colors as black and yellow/grey. The brake light switch (the black switch) has two purposes which explains 3 wires. The solid black wire is the power source. The black/orange is the power to the brake lights when the pedal is depressed. The third wire you see in the pic, black/red, is also for cruise cancel when the brake pedal is depressed. So at this point you have the correct switch purchased. You just have to replace the correct one under the dash. Hope this helps.

Thanks for the help. I could be wrong but it appears the part number you posted has two different versions. Round example like the pocket just above and the one we just bought. Anywho. I'll check the voltage as you mentioned.

I guess I am missing something then. The picture you show with the red arrows above is 100% the brake light switch. When I search the part number I list, it shows the same switch as you pictured with the red arrows. If there are any difference they could be design improvement's?

Using the brake switch part number in google. Ive found the round switch is 8-10 dollars and the square switch is 22-30. So, I'm hoping the connector will disconnect easily and connect to the square version. It's not my car so I'll access it again soon and let you guys know. Appreciate the help.

Update. Removed the junk cheap switch pictured and replaced it with the factory style PB posted previously. Easy job, just confused because of the older switch difference. Brake light issue resolved. Next problem. Turn signal light on dash stays on when the headlight switch is on. No issues when the headlight is off. Any ideas. Thanks

Headlight switch is a known failing part that causes weird things to happen.

Thanks for the quick reply. Is it better to rebuild it or buy a new one?

Update. Replaced the headlight switch and no change. Last week Replaced the brake switch which fixed the three rear brake lights issue. Issue continue: head light turned on , dash left signal is on , not flashing. If I use the left signal it won't work with the headlights on. With headlight switch on I noticed the PS yellow light is not on. If does flash when the right switch is enabled. I checked the ground wires for both front light. Clean as a whistle. I removed the PS headlight and plugged it back in. Is it a connection issue on the housing? My Cayenne has a similar issue and I just plugged it in manually instead of using the guide rail for the lights. Possibly wiring harness for the front or rear of the lights? I really doubt it's a relay for the lights. Any more ideas would be much appreciated!

So you changed out the headlight switch. Where did you get the headlight switch and what does it look like? There are correct ones and wrong ones. What was the part number?

Orileys auto parts with life time warranty. I'd assume it's a rebuild but have no idea. Stamped on the back - Made in Italy. I'm pretty sure the box number matched the original part but I'll verify. Color was silver and red. Replaced part with no change

Old part and box. I didn't take a picture of the new parts back but I do recall it had a made in Italy stamp.

Quotes source post: 15483725

my intital gut feeling is either a short of the wiring inside the headlight or tail light housing or the turn signal switch. i would disconnect both the head light assembly and tail light assembly for the effected side. Then turn on the headlights. If the turn signal light on the dash no longer lights i would suspect that. If it does i maybe an internal short in the turn signal / high/low beam switch.

I would open the back of the headlight assemblies and take a look. The previous owner of my car installed "better" bulbs that caused the housing to get hotter than normal. It yellowed the inner lens and made the insulation on the wires very brittle. The insulation on the wiring literally disintegrated when I touched it. There were bare wires touching each other.

Quotes source post: 15468348

Well, it looks like I now need to replace my headlight switch. Turned on my lights as I was heading out to work in the dark, and nothing. Had to fiddle with it to get them to turn on...

Changing my headlight switch out today as well. Headlamps, tail lamps and everything except the backlighting for the instrument binnacle was working fine. Used to be able to switch on/off, jiggle the switch and cross my eyes to make it work but finally done. We'll see if this solves the problem.

I've narrowed it down to the wiring harness for the DS tail light. Problem went away after disconnecting the tail light. Problem also went to other side when swapping the lights. Anybody want to buy a used headlight switch? 50 bucks shipped in US