Pressing Brakes Cuts Electrical

[smc]

Hello all. I am new to the forum and would appreciate any help you can offer.

I have a 1992 LS with about 102K miles. It has been cared for quite well by various dealers since I bought it used in 1996 with 63K miles. Problem is, every time I take it in for a problem like this I'm charged $325 or more, and I need to start trying to resolve these problems myself to save money and keep the car long term.

Several months ago I noticed that after driving long distances at speeds of 60 MPH or more, the front headlights would dim significantly right when I pressed the brakes. This only happened after driving for several miles without pressing them. Well, the problem has continued to get worse, now dimming them and simultaneously cutting out my stereo power for about 0.5-1.0 second when driving only short distances (several blocks) at 40 MPH. When the headlights go dim they stay that way, but are almost as bright as they should be. The thing that worries me now is what will cut out next, something critical? The key thing to remember is that everything is fine powerwise until I press the brakes!

The battery is about 3 years old and in generally good shape. The alternator has never been replaced to my knowledge. I really don't know how to check for shorts in the electrical system but I did check the brake lights and they all work fine, just one of the rear lic. plate lights is out. A guy at work told me that a bad brake bulb could be causing this problem, but I'm somewhat skeptical as I thought bulbs either work 100% or don't work at all, and rarely cause shorts. When the brakes are pressed, is there some sort of relay or electrical device that comes into play? I'm hoping this is the problem and it won't be an expensive repair. My second guess is that the alternator is faulty and somehow causing these symptoms.

If anyone has a good idea of the source of my problem, I would appreciate hearing from you!

Thanks, Steve C.

[SKperformance]

There are threads with the exact fix for your problem.

You have common short in the trunk wiring.

[90LS400Lexus]

Yep, SK is correct. Sounds like the old well-known trunk wiring problem. It is something about the wires around the trunk hinge shorting out. It can cause an array of woes. It can even cause flashing of the warning lamps.

[smc]

OK, thanks to both of you for the quick response. I believe I found the proper thread from 2003 re. this problem. I wasn't using the proper keywords in my first search. I will attempt the fix and let you know if I still have issues. Thanks again! SMC

[90LS400Lexus]

Excellent. Good luck. Let us know how it turns out.

[SKperformance]

glad you found it.

[ko90ls]

i was also having that problem (before i found this site :D ) so i just had to replace things that i thought were the issue, what cleared it up for me was when i did the tune up. wow what a difference. but for me i really happened when i hit the brakes hard, bottom line the tune-up fixed it

[AzHotLS]

smc, what key words did you use?

Edited: Never mind. I found it by doing a "+trunk +wire +short" search. Here is the link: http://us.lexusownersclub.com/forums/index...?showtopic=3821

[91L3xus]

This probably isn't the right page, but it's the right topic, so here goes.

My 2002 4Runner does the same thing of lights dimming when I hit the brakes, also the gear selection lights and clock will sometimes flash when I put on the turn signals. New Interstate battery less than 1 year ago. Could it be the same trunk short problem? Or would it be different because of the different model?

[90LS400Lexus]

When you say "flash" when you refer to the gear selector lights and clock- do you mean they also dim down, or actually go completely out? If they just dim, it sounds like a weak battery/alternator.

I doubt that the 4-Runner would have a short. The LS400 only does this because the wiring gets chafed near the hinge. I guess it is possible that they place some wires on the 4-Runner too that are vulnerable to chafing, but I doubt it.

This probably isn't the right page, but it's the right topic, so here goes.

My 2002 4Runner does the same thing of lights dimming when I hit the brakes, also the gear selection lights and clock will sometimes flash when I put on the turn signals.  New Interstate battery less than 1 year ago.  Could it be the same trunk short problem?  Or would it be different because of the different model? 

←

[SKperformance]

bad battery cables or alternator

[91L3xus]

(On the 4Runner)

What I meant to say is whenever I turn the signals on, the clock and gear selector lights dim in unison with the blinker; so when the arrow lights up on the dashboard, the clock and gear lights dim, then brighten when the arrow flashes off, until I turn off the signal. When I hit the brakes the headlights dim. Alternator checked out O.K. at an independent service shop. And like I said, new Interstate battery installed less than 1 year ago.

-------------------------------

On my '91, when I put up the windows, the gear selector light dims too, and more disturbing is that the RPM's drop. I'm guessing that's a problem with the alternator? Or something along those lines.

[smc]

Hello SKperformance and 90LS400Lexus, and now 91L3xus.

Well, last night per the 2003 thread solution I unwound the black tape around the wires and stabilizing brackets at that u-turn area where one of the wires is supposedly too short for the "trunk fully up pull distance" and found that the white-with-black-stripe wire of most concern was not broken or even chaffed. I could keep unwinding more black tape to and from that area but I believe I won't find anything, and just more to put back together.

I didn't mention in my original post that about a year ago the dealer had to replace the power steering pump because it was leaking on the alternator. I believed them bec. I had to keep adding more PS fluid every 3 mo's. If it was the alternator, however, I'd expect other power problems not associated with just pressing the brakes. Do you agree? I'd also like your opinion on that other potentially faulty device I mentioned which I believe is called a brake relay or actuator. I do hear it or another part click in every time I press the brakes. Can't recall if this is normal. It's not real loud. Could this "relay" have worn out over time and be causing a short in the electrical system? I believe I heard of this same problem with an old or defective turn-signal device that would come into play in say, 91L3xus's problem.

I also didn't mention that every other day I do get the Check Engine and Trac Lights coming on simultaneously for various amounts of time. Last time this happened 6 mo's ago it was a bad oxygen sensor, and I'm thinking/hoping that's all it is again this time. Once I can figure out where to get that diagnostic device which will display the problem codes (I read about in some thread), I'll attach and see if the current problem it's barking about could somehow be related to the brakes dimming headlights problem. Right now I'm thinking 50/50 chance. I'd also like your opinion on this.

Thanks! Steve C.

[90LS400Lexus]

Sorry to hear that you did all of that for nothing. I bet it is frustrating. Luckily, I did not have this problem with my 90' LS.

That "clicking" you are referring to when you depress the brake is normal if I recall. I think mine did it, as well as most other cars I have owned. I think that sound is just the lock releasing @ the shifter.

[smc]

Thanks for the reply 90LS. Yes, it was somewhat frustrating. With hot weather, black tape sticky stuff all over my fingers and some remaining on wires. Have sore hip from leaning into trunk also. Will put back together this weekend once I'm 100% convinced the problem is not in this area.

I'm thinking your correct about the clicking noise being the shifter lock releasing, but as I recall that only happens when I have the car in Park. I'll verify when I leave work now.

Will continue to work on the problem in the coming weeks before my next 300 mile trip, at which point I plan on using my new Escort detector which I don't want cutting out and eventually frying due to the on-and-off surges which I suspect will come in through the cig. lighter when I hit the brakes. I looked for a 12V car surge suppressor on line and didn't find one.

If anyone else reading this thread has any additional thoughts in regards to finding the root cause of my problem, I'd appreciate hearing from you, esp. on the last two opinions I asked of SK and 90LS.

Thanks, Steve

[SKperformance]

the radar has its own fuse in the plug so i would not worry about it.

If the lights seem to be dimming more than you feel is normal then i would change the battery cables as it is cheap and easy ( i have made complete posts for other cars on this board).

If it continues then the alternator needs to be looked at since you did have previous PS leaking on it.