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YOUR RESEARCHStrange problem: Turn on lights, both windows roll down
Leading reported evidence
Disconnect passenger window switch, the problem stopped
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Performed · outcome unconfirmed · Original poster
When I disconnected the passenger window switch, the problem stopped.
Strange problem: Turn on lights, both windows roll down
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Leading evidence: 'Disconnect passenger window switch, the problem stopped' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Disconnect passenger window switch, the problem stopped' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed
Such black boxes can be opened up, inspected, and solder reflowed or capacitor replaced, very inexpensively.
Strange problem: Turn on lights, both windows roll down
Replace headlight switch
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Strange problem: Turn on lights, both windows roll down
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I parked my car for a few days and had it on a battery tender.
This morning I got in, started it the engine, and turned on the headlights.
Immediately both windows rolled down and wouldn't roll back up.
If I turn the lights off, the windows will go back up.
I restarted the car and had the same issue.
So now, I can't drive at night with the windows up.
If it were not 100F(39C) currently then I wouldn't worry about it as much.
But I would worry about burning up the window motors as I think they're being powered constantly when the lights are on.
I've already ordered a replacement headlight switch this morning, but I'm not certain that will fix it.
Anybody ever had this issue before? (Search didn't find anything)
I hope it's not a BCM or power distribution issue.
About 2 or 3 months ago I had trouble turning the headlight switch off.
I really had to manhandle it to get it off.
I've been thinking about picking up a switch to have it handy anyways.
Just a quick glance at the wiring diagrams, I don't see much/if any interface between the lights switch and the windows. Maybe at the CU locking module, but not even sure about that! Honestly, the Porsche schematics drive me crazy and this after being a RR locomotive electrician in my long ago past. There are a few here that will know and hopefully will chime in.
Take the following with a grain of salt, since I don't yet have a 996 but do have fair experience with German (typically Bosch or Siemens) electromechanical systems: If your car has a light control module or somesuch other relay/module system for controlling various subsystems, you may have a bad capacitor or dodgy relay or module. When those go south, it's usually something simple like a hairline crack in a solder joint. Such black boxes can be opened up, inspected, and solder reflowed or capacitor replaced, very inexpensively. An $8 soldering pen from Harbor Freight will do wonders, or a 90 cent capacitor replaced if it's leaking.
I'm guessing your problem has to do with such a minor fault, which may come and go with temperature changes. (electronics board heats up, expands, opens hairline crack, quits working properly. Shut down, unit cools, crack closes, she works again until next heat cycle, etc.) There are shops which refurbish these units, for a stout price + your old unit as a core. You can do this yourself at a small fraction of the cost, if you have a steady hand and can bone up on YouTube on how to do this:
You Tube
I was thinking it sounded like a BMW footwell module.
I'm not certain if the 996 has a lighting control module, or if the BCM controls lighting or not.
Just recently started working on watercooled Porsches and haven't run into lighting issues...until now.
Our cars do strange things when the battery voltage is low, or some other malfunction. I don't honestly know how the light switch might relate to the windows, but stranger things happen with the light switch or ignition switch are involved. Perhaps pull fuse D1 to disable the windows until you get things sorted.
Well, I finished up work early today, so I got a chance to take a look at my own car for once.
I started by looking at the wiring diagram in the Bentley manual.
The only place I could find that the power windows and the lights were in the same location (other than the fuse box) was in the window switches themselves.
When I disconnected the passenger window switch, the problem stopped.
Luckily I had two window switches from a parted out Boxster that I was given some parts from.
I was able to fix my problem for free...except for the $140 I spent on the light switch that's headed my way.
I'm trying to decide if I should keep the switch, install it in my car, and save my used one for the next customer car that needs a switch ASAP.
Of course I'd sell it cheap, or let them use it until they get a switch of their own...or likely give it to them.
Also I ordered a Key upgrade...and had it all sent to me via 2nd Day Air.
A cheap fix sure cost me a lot today.
Working on Porsches is a LOT more fun than working on BMWs!
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