Brake Lights Operating Backwards

[leswhiting]

I have a 1999 996 C2 Coupe (CANADA) Car with Daytime Running lights. When I put the key in the ignition and turn to accessory or start the car, all my brake lights turn on. Both drivers, passenger side and brake light in wing turn on. When I apply the brakes the lights then go out. Essentially they are opreating backwards!??

All my turn signal light, headlights etc seem to be working properly. I've checked all my fuses and everything seems good. I had a quick look at the switch on the brake pedal and all the connections seem to be good.

I'm hoping someone has encountered this problem in the past and might have some suggestions.

Thanks

Les

[stickshiftnz]

When the ignition is off, and you step on the brake pedal, do the lights come on normally? I was going to suggest there may be a grounding issue with one of the lights, but if all three of them turn on, it would be something centralised. If the car has some lighting system black box, you may wish to check that out.

[wwest]

I have a 1999 996 C2 Coupe (CANADA) Car with Daytime Running lights. When I put the key in the ignition and turn to accessory or start the car, all my brake lights turn on. Both drivers, passenger side and brake light in wing turn on. When I apply the brakes the lights then go out. Essentially they are opreating backwards!??

All my turn signal light, headlights etc seem to be working properly. I've checked all my fuses and everything seems good. I had a quick look at the switch on the brake pedal and all the connections seem to be good.

I'm hoping someone has encountered this problem in the past and might have some suggestions.

Thanks

Les

Canadian DRLs include street/marker/parking/tail lights being on. I would look for loose grounds.

[wvicary]

Do you have the factory relay installed for DRL's? I have seen many aftermarket kits installed incorrectly.

[leswhiting]

When the ignition is off, and you step on the brake pedal, do the lights come on normally? I was going to suggest there may be a grounding issue with one of the lights, but if all three of them turn on, it would be something centralised. If the car has some lighting system black box, you may wish to check that out.

No, the brake lights do not come on if the ignition is off. I'll check all the bulbs and ground wires and see if I can find anything.

[leswhiting]

Do you have the factory relay installed for DRL's? I have seen many aftermarket kits installed incorrectly.

Yes this is factory installed DRL's as this is an original Canadian Car.

[Loren]

Perhaps someone installed a new switch on the brake pedal?

[Orient Express]

When did this start, and what changed around then?

[leswhiting]

When did this start, and what changed around then?

Loren / Orient - This is an intresting little problem, annoying as well. No new switch has been installed and no work done on the car at all. It just started doing this recently. I have had intermitten issues with my lights and tail lights and I have to think it is somehow related.

Sometimes when I turn the car off but keep the key in the ignition the drivers headlight and tail light will remain on, however the passenger side headlight and tail light will not be on. When the car is started however they both turn on.

I'm not entirely sure if this is normal or not, but again it's intermitten.

[wvicary]

Remove the DRL relay and see if the problems continue.

[wwest]

When did this start, and what changed around then?

Loren / Orient - This is an intresting little problem, annoying as well. No new switch has been installed and no work done on the car at all. It just started doing this recently. I have had intermitten issues with my lights and tail lights and I have to think it is somehow related.

Sometimes when I turn the car off but keep the key in the ignition the drivers headlight and tail light will remain on, however the passenger side headlight and tail light will not be on. When the car is started however they both turn on.

I'm not entirely sure if this is normal or not, but again it's intermitten.

Your Porsche blue with grey interior BBS wheels...??

[leswhiting]

When did this start, and what changed around then?

Loren / Orient - This is an intresting little problem, annoying as well. No new switch has been installed and no work done on the car at all. It just started doing this recently. I have had intermitten issues with my lights and tail lights and I have to think it is somehow related.

Sometimes when I turn the car off but keep the key in the ignition the drivers headlight and tail light will remain on, however the passenger side headlight and tail light will not be on. When the car is started however they both turn on.

I'm not entirely sure if this is normal or not, but again it's intermitten.

Your Porsche blue with grey interior BBS wheels...??

Nope it' Arctic Silver with Black Interior.... I checked again with a helper so I could see what was going on with the lights and found out the following. Any thoughts?

1. When the car is OFF and no key in the Ignition, the brake lights do not work, any of them.

2. When I start the car or with the key turned to on, the brake lights (ALL) come on and when I hit the brake pedal, all brake lights go off.

3. When I turn the car off, but leave the key in the ignition in the off position the brake lights go off and the passenger side taillight and headlight go out. Turn back to on or star the car and both lights come back on and so do the brake lights!! VERY FRUSTRATING and not SAFE...

Appreciate any help people can offer who have better understanding of the electrical system that I....

[Loren]

Unless there is a short in the wiring somewhere it almost has to be the brake light switch.

[RFM]

I would give it a try with a new BROWN colored brake light switch.

[leswhiting]

I would give it a try with a new BROWN colored brake light switch.

Is that a joke or is there a newer version coloerd brake switch? Any chance you would have a part number and I think I'll try ordering from Sunset..

[Loren]

I would give it a try with a new BROWN colored brake light switch.

Is that a joke or is there a newer version coloerd brake switch? Any chance you would have a part number and I think I'll try ordering from Sunset..

No joke.

996.613.113.02 is the latest switch.

[leswhiting]

I would give it a try with a new BROWN colored brake light switch.

Thanks RFM. I see what you mean now about the BROWN switch. Red Switch is for the clutch. I'm going to swap it out as I think it has to be a faulty switch.

[leswhiting]

I would give it a try with a new BROWN colored brake light switch.

Thanks RFM. I see what you mean now about the BROWN switch. Red Switch is for the clutch. I'm going to swap it out as I think it has to be a faulty switch.

Tried replacing the brake switch but this did not fix the problem. I've checked the ground and it's good. All bulbs are good with no signs of any corrossion at the connectors. Next I' guess I'll start having to look at relays to see if they somehow control the brake lights. I believe S6/7 is the DLR relay. I've got a list of the relays from the dealer but they don't give much detail on what they control. Some simply say RELAY.

Appreciate if anyone has any thougths on which relays I ougt to look at.

Thanks.

[wrljet]

re: Backwards brake lights. Here's how that happens.

None of this may apply to your problem, and I haven't looked at the wiring diagram yet...

Taking the 911 out of the picture, assuming a fairly generic wiring setup for tail lights for a second...

Often, rear running/parking light is a low wattage filament, and the brake light is a brighter wattage

filament in the same bulb. They share a common ground. Typically in an older American car

a #1157 lamp was used.

Now assume a ground has gone bad over the years from corrosion.

Light switch OFF. If you hit the brake, power comes from the brake light switch to the higher

wattage filament. It has no ground, so goes through the parking light filament and then back-powers

the entire rest of the parking light system.

Generally the parking light system includes quite a few bulbs. Assume some of these still

have their grounds. The back powered parking light system now powers all the remaining

bulbs that have grounds. The combined parallel resistance of these will be low. Powered

-through- that one original filament that had no ground, which is a higher resistance, not

much current exists in each of the lamps. So they don't glow brightly. Perhaps not visible

in daylight. BUT, combined in parallel their combined current is enough for the original

brake light to show up.

Thus a car with a bad ground on one tail light can still have that brake light function

during the day.

Now assume you turn on the parking lights.

The reverse happens, and the brake light system is back-powered. But the resistance

ratio between the low and high current/brightness bulbs is reversed. So the tail light

works. Then you hit the brake pedal. Juice comes from brake light switch to the

bulb filament, killing the fake ground path, so now there is +12 on both sides of the

tail light bulb at the socket with the bad ground. The symptom now is all lights at

that socket appear to go out.

----

Adding DRL to the picture, does turning on the key in a car with DRL normally cause the

rear running lights to come on?

Bill

[leswhiting]

re: Backwards brake lights. Here's how that happens.

None of this may apply to your problem, and I haven't looked at the wiring diagram yet...

Taking the 911 out of the picture, assuming a fairly generic wiring setup for tail lights for a second...

Often, rear running/parking light is a low wattage filament, and the brake light is a brighter wattage

filament in the same bulb. They share a common ground. Typically in an older American car

a #1157 lamp was used.

Now assume a ground has gone bad over the years from corrosion.

Light switch OFF. If you hit the brake, power comes from the brake light switch to the higher

wattage filament. It has no ground, so goes through the parking light filament and then back-powers

the entire rest of the parking light system.

Generally the parking light system includes quite a few bulbs. Assume some of these still

have their grounds. The back powered parking light system now powers all the remaining

bulbs that have grounds. The combined parallel resistance of these will be low. Powered

-through- that one original filament that had no ground, which is a higher resistance, not

much current exists in each of the lamps. So they don't glow brightly. Perhaps not visible

in daylight. BUT, combined in parallel their combined current is enough for the original

brake light to show up.

Thus a car with a bad ground on one tail light can still have that brake light function

during the day.

Now assume you turn on the parking lights.

The reverse happens, and the brake light system is back-powered. But the resistance

ratio between the low and high current/brightness bulbs is reversed. So the tail light

works. Then you hit the brake pedal. Juice comes from brake light switch to the

bulb filament, killing the fake ground path, so now there is +12 on both sides of the

tail light bulb at the socket with the bad ground. The symptom now is all lights at

that socket appear to go out.

----

Adding DRL to the picture, does turning on the key in a car with DRL normally cause the

rear running lights to come on?

Bill

Hi Bill,

Thanks for the very detailed explanation. All makes sense to me and I guess I could test with a volt meter to see if I am getting any voltage at the brake light connector when I apply the brakes with the key off.

Any suggestions on how I may check this and how I may try to isolate a bad ground. The car is in very good shape, the battery is new (1 year), the terminals are all very clean. I pulled the tail lights and checked all the connectors and they too seemed to be in excellent condition with no signs of any corrossion.

I'm not sure about the DLR question, but the more I think about it maybe the rear tail lights don't come on with the DLR but they are now. I'm going to try pulling the DLR relay and see what happens.

I'll let you know what I find out and welcome any tips to help isoloate this...

Thanks...

[JeTexas]

If it's a bulb filament causing ground, you should be able to test by removing one bulb at a time and checking for changes in the symptoms.

[wrljet]

Any update on your problem?

[leswhiting]

Any update on your problem?

Update on this problem. After trying pretty much everything I could imagine with absolutetly no success, I resorted to changing the light switch but this did not resolve the problem.

I decided I would try another new brakelight switch from the dealer and the problem was corrected. I disassembled the brake switch which was purchased new from the dealer and found a defect in it. Very frustrating but glad I got the brake lights working.

[RFM]

This double action switches are indeed very fragile inside.