Need help, odd tail light behaviour

Have done some research a few times and have tried a few things, but now I'm stumped and could use some help. Around the holidays one of my nice co-workers stopped me to point out that my passenger side tail lights were out, so I swung by the parts store at lunch and replaced them. About a week later one of my friendly neighbours pointed out the same thing, and I said, "but I just replaced them...". I checked them later that day and they seemed fine to me. Then I discovered the problem, asked a fellow owner for their thoughts and got even more confused. Here is what's happening: On the driver side, the two outer lights of the tail light are on all of the time, regardless of whether or not the parking or head lights are selected on the switch. On the passenger side, the two outer lights only turn on when the parking/headlights are selected. I had assumed something was wrong with the passenger side, maybe I got the wrong type of bulbs or maybe a fuse was out. I've checked the obvious fuses A3,A4, etc and they are fine, and I've swapped the bulbs and the behaviour remains. It was about that point where the other owner that I spoke to suggested the problem was that the driver side lights shouldn't be on all the time. As it's a Canadian car (hello from the great white north), I assumed that they should be on as part of the daytime running lights, but that owner was insistent that only applied to the headlights. So now I'm not sure which problem I'm trying to fix or what other possibilities I should start with. Any help is deeply appreciated. And if my Google-Fu is weak and this problem is already solved elsewhere please don't hesitate to link it. Much appreciated.

You may wish to check the inside of the lamp sockets. The 'made in Poland' bulb holders and wiring harness is notoriously problematic (read:CHEAP) and the electrical spring contacts can break off and go missing or get wedged inside the socket and cause a short. Note - Posting the year of your car may be helpful to other forum members if my suggestion does not assist.

Thanks for the tip, it's a 2002 996 C4 Cab, doubt the C4 Cab is helpful in this context but just in case. As for the sockets, nothing stood out to me, I'll look more closely and post back. That said, is that for the side where the lights aren't on, or where they are on all the time? I'll check them both. JJ

FastM96 is right about the tail light wiring harnesses, so check them closely for the broken center contacts. Usually this will blow fuse or prevent lights from ever coming on in bad side so not sure this is your problem as I think you mean they will come on with right switch positioning.(?)

Jas: re-read your post...not sure if Canadian cars are different than USA models, but the "parking" position is for parking at a curb and it only illuminates the car left front parking and left rear lights so other drivers can see your car clearly. To actuate this feature on my 2005 996 C4S the headlight switch must be pulled out and then turned to left. Don't believe this position is for driving. Sounds to me that there is nothing wrong with your car. Correct me if I misunderstand your post.

That's good to know about the parking light being driver side only. Makes complete sense. However, the behaviour happens with the headlights as well. That is, everything works properly when the headlights switch is on. However, when they are off, the driver tail light is still illuminated. I can post some pictures once it gets darker here. Haven't had a moment to check the hardness yet. Really appreciate all the replies.

Had a chance to review the bulb holders and wiring hardness. Nothing looks out of the ordinary with either. I checked the hardness connector but I didn't cut off the label (which does say 'made in Poland') or the shield to examine the actual soldering. Let me know if that's what I should be doing. Also noticed some new behaviour, to summarize and reduce some of the confusion. Here are the states: 1) Key in ignition, before starting car: no tail light are on 2) Car is running, no changes to headlight switch: driver side tail lights are on 3) Headlight switch set to on (car can be running or off): both passenger and driver side tail lights are on 4) Key in ignition, car is off, but had been running: driver side tail lights are illuminated

Is it true when the tail light on one side is on, the front parking light on the same side will also be on? The power to the tail lights are supplied by the light switch and the DRL relay. Either one is on, the tail light will be on. Sounds like your DRL relay is bad as it has individual contact points to the left and right tail lights. Or the cable from the DRL to the right tail light is open. You may want to remove the relay and bench test it. You will need a multimeter and some basic electrical trouble shooting skills.

Jashva: Listen to Ahsai, he knows his stuff!

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If the turn signal lever is down (indicating left turn) and you shut the car off the left side parking lights will stay illuminated. Same thing happens on the right side if the lever is up when you shut off the car - this has been part of Porsche (and maybe other Euro makes) for 30+ years. Try it when you park in the garage one time.

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Thanks Billy.

Ahsai: Just sharing the facts...

Thank Ahsai. I'll check out the relay and post back. Just to be clear, you are agreeing that the passenger side should be lit and that's the problem side of the relay? Thanks again all, this has been extremely helpful.

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I agree as long as your headlight switch is at the OFF position. When the DRL is activated, both tail lights should be on.

Also check out this thread. Do you have LED tail lights? https://rennlist.com/forums/996-forum/678644-daytime-running-light-problem-with-led-tail-lights-solved.html

Thanks for all the advice so far. No LED headlights, they are just the Xenon ones (or at least I think they are). I've finally figured out which relay it is and removed it. 996.615.111.00. I'm aspiring to get better with electronics, so I have the necessary tools and basic understanding, however, little familiarity with relays. Youtube helped get some insight on that. Unfortunately the DRL relay is a bit more complicated that I expected. Each side has 5 pins rather than 4. And of course the relay doesn't have a diagram (and I can't find one online) and the only description that the relay has on it is in... german, not that it would help much as the only word used in the pin descriptions is 'klemme' which I guess means clip. So I'm not sure how best to test this, that is I'm not sure which pins to energize and I'm not sure if all the paths are protected by diodes, so I'm hesitant to just start energizing. Has anyone happen to come across any instructions, diagrams, etc for testing this specific relay? If not, I'll likely just order up another one and hope for the best. JJ

Spoke a bit too soon. Have discovered this diagram which I suspect holds the answers, after I decipher it...

Still trying to figure out which pins to energize to test, but realized that if any were stuck open I should be able to see that in there being resistance between pins. I quickly compared each pin to every other pin and found nothing, so at least the relay isn't stuck open. So it's a start. If I can't figure this out shortly, I'll likely just order a replacement relay. Given my symptoms and how the relay is wired and what it does, I'm feeling pretty confident that we've found the problem. At this point, it's more about the satisfaction of confirmation and posterity.

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If you can wait, I can help once I can access the wiring diagram later today.

Much appreciated, and no rush. I wasn't was going to order it today. The dealership is closed until Monday anyway, and I've got the other Porsche owner giving me a hand with testing it tonight. He's a radio engineer so he's far more knowledgable on electronics than I.

You've got PM.

I think we've got it. I still didn't have great luck interpreting the diagram. Unfortunately the numbers on the bottom of relay don't correspond to the numbers on the diagram. There appears to be a mapping label on the relay, but it wasn't entirely clear either, that is, some of the numbers matched up but not all. Anyway, we popped the cover off the relay, start looking at the circuit board to deduce the connections and realized that some of the solder joints weren't looking too healthy. Fix the joints and voila consistent behaviour. Now all the lights are on while the car is running. I'm still not clear if they are all supposed to be on, or just the front ones, but at least they are consistent and my neighbours won't think that I'm ignoring their courteous notification of my dead bulbs. Thanks again for your help all. I'd have never even considered the relay without you and I'd have probably be out $100 to have replaced the unit even if I had figured it out. JJ

Satisfaction of successful diagnostic and repair. A lot of time it's not about the $

Btw, the pin number mapping is in these photos. Hopefully you won't need these anytime soon https://www.ecstuning.com/b-genuine-...y/99661511100/