Apply brakes and the headlights turn off...
10-26-2008, 02:01 AM
#1
Apply brakes and the headlights turn off...
I had an annoying problem tonight: my headlights would turn off whenever I stepped on the brake and come back on a moment or two after I released the brake.
The headlights remained raised up, and the driving lights were unaffected when this happened, but there might be other symptoms I did not notice. It was late so I did not even try to troubleshoot it.
Has anyone had this strange problem before? If so, what was the cause? This reminds me of the very weird and sometimes humorous electrical problems a friend's ancient Austin Healey Sprite used to have
Thanks.
PS - FWIW, the car is an '89GT
The headlights remained raised up, and the driving lights were unaffected when this happened, but there might be other symptoms I did not notice. It was late so I did not even try to troubleshoot it.
Has anyone had this strange problem before? If so, what was the cause? This reminds me of the very weird and sometimes humorous electrical problems a friend's ancient Austin Healey Sprite used to have
Thanks.
PS - FWIW, the car is an '89GT
10-26-2008, 11:36 AM
#2
Electron Wrangler
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Well its sounds like a grounding problem - whenever 2 unrelated systems start interacting that is always the first suspicion. Clean/tighten all grounds (esp at CE panel).
Alan
Alan
10-26-2008, 12:07 PM
#3
Team Owner
what was the last thing you fixed??
10-26-2008, 01:52 PM
#4
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Not to poke fun--but that's a ridiculous problem! I've been getting seriously teased by friends/family that thought I was silly to by a 17yr old car--good friend/next door neighbor just bought a new Lexus and keeps hasseling me when my shark does something weird like this--I don't think I would hear the end of it if I headlights went off went I braked. Good luck, can't wait to hear what turns up once you start tracking this down.
10-26-2008, 04:02 PM
#5
Thanks for the quick responses.
"Not to poke fun--but that's a ridiculous problem!" I agree completely. Not that I wish to offend anyone here, but I thought that stuff like this only happened to English cars....
I realized that I had not described a couple of other symptoms last night, so FWIW, they are (in addition to the headlights being extinguished as long as the brake pedal was depressed): the stop lights did not come on when the brake pedal was pressed; and the main high beams would not come on at all. Shutting the engine off by turning the ignition switch to the accessory position without turning all of the way to off restored full headlight function (high and low beams worked as selected and were unaffected by the brake pedal), but the stop lights still did not illuminate. I did not restart the engine and retest.
I do not have time to actually start dealing with the problem until tomorrow, but I wanted to confirm the problem and try some other combinations of switch settings... Guess what? The only problem early this morning was that the stoplights do not work at all (with engine running). Everything else seems normal.
I had removed the CE panel about a year ago to clean and tighten up the fuse contacts and the ground connections, but I will certainly go through the grounds again. The last serious work done was an intake R&R. Prior to that it was new vacuum actuators (all except the one under the pod - don't want to have too much fun all at once...). Everything checked out after each surgery and had been working well (I think).
Is there any chance that the "bulb control unit" could cause this? I briefly looked at the schematics, and it looks as if it is directly involved in the stop light function (not just a monitor?), but I did not trace the headlight circuits out... too many twists and turns and a non-928 schedule to keep. The BCU and its cabling got moved around when the passenger's parcel tray was removed and replaced, but the connections seemed clean and bright and were treated to a spray of Deoxit before reassembly.
I don't know if any of the above is helpful, but I do appreciate the assistance.
UPDATE: One more recheck, and guess what? Everything seems to work correctly now. There was no poking or prodding of wires, relays, connections; only the manipulation of switches. Real hard to find a problem like this.
"Not to poke fun--but that's a ridiculous problem!" I agree completely. Not that I wish to offend anyone here, but I thought that stuff like this only happened to English cars....
I realized that I had not described a couple of other symptoms last night, so FWIW, they are (in addition to the headlights being extinguished as long as the brake pedal was depressed): the stop lights did not come on when the brake pedal was pressed; and the main high beams would not come on at all. Shutting the engine off by turning the ignition switch to the accessory position without turning all of the way to off restored full headlight function (high and low beams worked as selected and were unaffected by the brake pedal), but the stop lights still did not illuminate. I did not restart the engine and retest.
I do not have time to actually start dealing with the problem until tomorrow, but I wanted to confirm the problem and try some other combinations of switch settings... Guess what? The only problem early this morning was that the stoplights do not work at all (with engine running). Everything else seems normal.
I had removed the CE panel about a year ago to clean and tighten up the fuse contacts and the ground connections, but I will certainly go through the grounds again. The last serious work done was an intake R&R. Prior to that it was new vacuum actuators (all except the one under the pod - don't want to have too much fun all at once...). Everything checked out after each surgery and had been working well (I think).
Is there any chance that the "bulb control unit" could cause this? I briefly looked at the schematics, and it looks as if it is directly involved in the stop light function (not just a monitor?), but I did not trace the headlight circuits out... too many twists and turns and a non-928 schedule to keep. The BCU and its cabling got moved around when the passenger's parcel tray was removed and replaced, but the connections seemed clean and bright and were treated to a spray of Deoxit before reassembly.
I don't know if any of the above is helpful, but I do appreciate the assistance.
UPDATE: One more recheck, and guess what? Everything seems to work correctly now. There was no poking or prodding of wires, relays, connections; only the manipulation of switches. Real hard to find a problem like this.
10-26-2008, 04:03 PM
#6
Rennlist Member
Good question, Stan -- this often provides some clues. 
Wiggle the key in the ignition switch with the lights on, at rest and while braking. Any change? (I would think the driving lights would also be affected if this were the issue, but try anyway)
With the lights on, pull forward on the headlight buckets. Any change? There is a switch inside the motor assembly that allows the lights to illuminate only when the motor is in the correct position.
Access the CE panel and see if lightly tapping/wiggling the light relay has any effect.
If none of the above -- check the ground points as Alan says. In fact, you should do this periodically anyway. Maybe it's overdue.
Wiggle the key in the ignition switch with the lights on, at rest and while braking. Any change? (I would think the driving lights would also be affected if this were the issue, but try anyway)
With the lights on, pull forward on the headlight buckets. Any change? There is a switch inside the motor assembly that allows the lights to illuminate only when the motor is in the correct position.
Access the CE panel and see if lightly tapping/wiggling the light relay has any effect.
If none of the above -- check the ground points as Alan says. In fact, you should do this periodically anyway. Maybe it's overdue.
10-26-2008, 04:10 PM
#7
Nordschleife Master
100% SURE this is your ignition switch. About $75 and you have to remove the pod to install... It will fix ALL your crazy unrelated problems.
Do you also have the funny noise from behind the dash when you hit the brakes that sounds like a vacuum leak or something like that??? I had that one...well, it only happens when the car is acting up. You can buy yourself a little bit of time by starting the car and then backing the key off JUST A TOUCH (w/o turning the car off obviously)... That worked for me for several X000 miles on my '88 S4!
Easy fix and now you know what it is!
Do you also have the funny noise from behind the dash when you hit the brakes that sounds like a vacuum leak or something like that??? I had that one...well, it only happens when the car is acting up. You can buy yourself a little bit of time by starting the car and then backing the key off JUST A TOUCH (w/o turning the car off obviously)... That worked for me for several X000 miles on my '88 S4!
Easy fix and now you know what it is!
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10-26-2008, 05:24 PM
#8
Team Owner
if your going to replace the ignitoin switch make sure to disconnect the battery first
10-26-2008, 10:33 PM
#9
Addict
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ROTFLMAO...sorry man, but that has to be one of the funniest issues I have heard in relation to a 928. I wish I could share the visual I got from this!
10-26-2008, 11:55 PM
#12
"ROTFLMAO...sorry man, but that has to be one of the funniest issues I have heard in relation to a 928. I wish I could share the visual I got from this!" - Yes. Picture this: driving somewhat .. quickly..; it is very dark; sweeping turn with no other traffic and no highway lights; touch the brakes and the lights go out...
No real danger as the road is very familiar and the driving/fog lights were on, so it was not a complete fade to black. My initial reaction was more embarrassment about the perversity of the problem than aggravation (maybe, since it is close to Halloween, the spirit of Lucas visited me for what I have said while working on British cars and motorcycles?). I did not wish to attract any attention from the constabulary or ridicule from anyone else: "Yes, officer, my headlights always go out when I apply the brakes.... it is a feature on German cars. After all, why would you use brakes anyway when you have a perfectly good horn? The brakes are only used as a last resort, so the lights go out when they are applied just in case you can not stop in time. It is merciful that way: you don't see what you are going to hit."
Problem Update:
Many thanks to everyone who responded.
It looks as if it might be the ignition switch: wiggling the key would sometimes cause the head lights and stop lights to go off, while another slight nudge would turn them on again.
I could not duplicate the exact symptoms (head lights off when brake pressed), but the switch is definitely bad. With any luck, the switch might be the only problem... at least for today...
I will get a switch on order, installed and post a follow-up; hopefully in the not-too-distant future.
I have no idea how long it would have taken me (if I could have found it at all) to find this out. Again, many thanks.
Bob
No real danger as the road is very familiar and the driving/fog lights were on, so it was not a complete fade to black. My initial reaction was more embarrassment about the perversity of the problem than aggravation (maybe, since it is close to Halloween, the spirit of Lucas visited me for what I have said while working on British cars and motorcycles?). I did not wish to attract any attention from the constabulary or ridicule from anyone else: "Yes, officer, my headlights always go out when I apply the brakes.... it is a feature on German cars. After all, why would you use brakes anyway when you have a perfectly good horn? The brakes are only used as a last resort, so the lights go out when they are applied just in case you can not stop in time. It is merciful that way: you don't see what you are going to hit."
Problem Update:
Many thanks to everyone who responded.
It looks as if it might be the ignition switch: wiggling the key would sometimes cause the head lights and stop lights to go off, while another slight nudge would turn them on again.
I could not duplicate the exact symptoms (head lights off when brake pressed), but the switch is definitely bad. With any luck, the switch might be the only problem... at least for today...
I will get a switch on order, installed and post a follow-up; hopefully in the not-too-distant future.
I have no idea how long it would have taken me (if I could have found it at all) to find this out. Again, many thanks.
Bob
04-06-2012, 12:46 AM
#15
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Wow, am I glad I found this thread. I thought I was going crazy. I brake, the lights go out, and I get a vacuum leak noise coming from the dash. I would have never guessed it would be the ignition switch. Any idea why that happens?