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My bet is a short in your connectors or maybe wire harness. As there is not any way for the lights to turn on from the ign switch unless the light switch is already on, (or you have auto on lights in a 996 ?) Just as there is no way for the light switch to feed back to the ign switch to keep engine on, unless both switches were shortedsimultaneously. But it would take both switches to be bad at the same time, and you already changed out the ign switch and have the same problem again... And with the plethora of unrelated fault codes it indicates a intermittent short, imo....
The way that switch looks, looks like it was water damaged, looks like it has rust coming out of it. And the back side of it is nasty like it maybe got real hot. That switch needed to be changed out for sure, you did the right thing changing it.
Was your car in a flood, or left out in rain with top down...?
That looks more like dielectric grease on the non-terminal end.
The terminals just look like normal 20 year old copper.
Maybe, but I've never seen brown rusty colored dielectric grease. Most switches I've worked on have a white or clear grease.
As for the terminal end, ya it does look like a 20 year old switch that was in the engine compartment not under the dash. To me it looks like some of that grease leaked out when switch got real hot.
Regardless of ign switch looks, still think there is a intermittent short. I'd start by taking apart all connectors in that circuit and cleaning lubing them and reassembling them correctly, while looking for chafed wires....
Which brand of ignition switch did you replace it with?
Just curious.
URO parts. I actually had two in the garage so I tried them both and the problem persists. Maybe I should try an OEM part just to be 100% sure, but I've had decent luck with URO.
I am suspecting the headlight switch because of the very odd behavior. It is like, once the car is running, the headlight switch becomes the primary ignition. I can remove the car key, and the car will stay running, but when I turn the headlight switch to off, the car turns off normally. Subsequently when I turn the headlight switch back to on, the car regains accessory power, even without the key in the ignition.
I ordered the headlight switch and the brake pedal sensor from pelican yesterday because I'm comfortable with the price and replacing them, should be here tomorrow. If the problem persists after that I will have to start looking for a short in the harness but that doesn't sound like a lot of fun!
I find Üro to be of decent quality also.
I replaced my headlight switch with a Üro when I thought mine was a problem.
My windows kept rolling down and then freaking out when I turned on my headlights.
Turned out to not be the headlight switch.
I had a short in the wiring to the driver side window switch.
That was an easy fix and now I can drive in comfort in hot or cold weather with my headlights on.
I gave my old factory headlight switch to a famous Youtuber (named after either a picnic basket stealing bear or a famous baseball player) and bought a spare Üro in case I ever need it.
I gave my old factory headlight switch to a famous Youtuber (named after either a picnic basket stealing bear or a famous baseball player) and bought a spare Üro in case I ever need it.
That brown stuff is the assembly grease. They are all like that.
The headlight switch absolutely can backfeed the ignition circuits. It has both unswitched power and switched ignition power.
Looked at wiring diagram, You're correct, there is unswitched power at headlight switch. Didn't know that, thanks for setting me straight. So yes, shorted out headlight switch could back feed ign switch....
Replaced the headlight switch and brake pedal sensor. And my problem persists. So, for those of you that called a short in the wiring harness early on, looks like you were right and I wasted $100 throwing parts at it. Now, how will I go about diagnosing this short. A few things are consistent:
1) Everything functions normally if the headlights are off.
2) If the car is stationary, and I turn on the headlights, nothing happens.
3) If the car is running, and the headlights are on, and then I start driving, I get "ABS Failure" "PSM Failure" "Drive to Workshop"
4) If I remove the key from the ignition the car stays running. If I turn the headlights to off, it kills the engine.
I do have a multimeter and what I would consider beginners electrical knowledge. I checked fuses related to ABS and Traction Control as a first step, and they look okay.
"Disconnect headlight switch, and ignition switch, and see if you have continuity between the headlight circuit and the ignition 'on' circuit."
I will try this next, I guess I am just confused which hole in the ignition harness to stick the probe, and likewise on the headlight harness, but I suppose I could trial and error.
"Maybe a ground connection."
This I don't understand, not that you're incorrect. I just don't understand how to test this.
Thanks in advance for any replies. I'm kind of stuck for now so any suggestions welcome.
another thing I noticed is my cruise control seems to turn itself on randomly and the clutch pedal doesn't turn it off.
So I figured I'll throw another $20 at the problem by way of a clutch pedal switch. At least when I eventually take it to the shop i'll be able to tell them I already replaced all the switches.
Have you checked any relays? Maybe a relay is sticking in the “on” position. From what I’ve figured doing my motor swap all relays stay on for approximately 10 seconds after key is in the off position. Whatever is happening is keeping your ecu circuit alive regardless of the key position.
