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Old 06-15-2008, 12:01 AM   #1
#522
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Default Stereo clock dims when pressing brake pedal

When driving, with the main lighting switch in the off position, my stereo (stock) clock dims and my brake lights are not very bright. When I switch the lights to on (either by turning the end of the stalk or using the parking light switch) the headlights, front corners and rear plate lights come on, but my 2 main rear lights do not. But the 3rd brake light is on all the time, even when I brake. I checked the bulbs in the back and they appear to be OK, both filaments are intact in each and taking one or the other out has no effect.

A while back, one of the bulb sockets' ground came loose, and caused that one light no to work, and the stereo to dim. I fixed and all was normal until 2 days ago.

This sounds like a bad ground or short to me, not a fuse or relay. I have pulled and checked all the fuses I thought were relevant, but plan to pull all of them tomorrow.

I do have 2 prosport gauges hardwired into the stereo harness for 2 years, so I will be checking that too, in case something came loose.

Just wondering if anyone sees this and says "oh yeah, i had this exact same, random problem and it was XYZ that fixed it..."

Any thoughts? Should I start in the back, or start with the stereo? Thanks!

Car is 2001 Impreza RS Sedan
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Old 06-15-2008, 02:33 AM   #2
Cougar4
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Check the grounding between the chassis and the battery. You may want to also clean the battery connections. If the problem is still occurring then check the rear grounding.
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Old 06-15-2008, 01:24 PM   #3
#522
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Thanks. I will check those first, although it looks like all the rear lights connect to the ground back there, and all the others work fine.
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Old 06-15-2008, 02:26 PM   #4
Mulder
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There is a cross-connection between the parking light and brake light circuits. When you step on the brake the parking light filaments in the rear bulbs are lighting instead of the brake filaments, and because the parking light circuit is being activated the clock dims as if you had turned the lights on.
You need to spend some time with the wiring diagram and a meter or test light.
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Old 06-15-2008, 04:06 PM   #5
Cougar4
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Mulder is correct about the cross-connection. To help find which circuit is involved you could start pulling fuses one at a time and see which one makes the 3rd brake light turn off.

It is strange that only the middle brake light is turning on since all three brake lights should be connected together. It must be seperated somehow from the others.

Last edited by Cougar4; 06-15-2008 at 04:15 PM.
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Old 06-15-2008, 05:50 PM   #6
#522
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I asked a mechanic friend about that, and he said it's possible they are on different circuits, in case something happens to one circuit, the other still works, to some degree.

Thanks guys, I never thought about it the way Mulder explained it, makes perfect sense now. I'll update as I find stuff out.
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Old 06-15-2008, 09:14 PM   #7
Cougar4
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That data that I looked at shows it on the same circuit.
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Old 06-16-2008, 01:03 AM   #8
#522
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it seems to be, yes. I did pulls fuses until the light went out, it was on the top row, #5 "tail clearance". I checked the ground in the trunk, and it is fine.

So in my searching, I found that the white wire/black stripe leading to the RH combo bulb (brake/taillight) had a slit and it could have been shorting to the metal lip around the rear light assembly. So I wrapped it up, and swapped the bulbs with new ones and nothing changed.

Is it possible it did short and damage a relay? Or would a fuse have popped? the RH bulb filaments are fine, but the bulb was a little dark.

Anyway, I'll look at it some more tomorrow.
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Old 06-16-2008, 05:13 AM   #9
Cougar4
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Check the trailer connector for a problem. Also check the wiring to the brake lights and follow it back towards the front as much as you can.
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Old 06-16-2008, 11:33 AM   #10
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Check every possible scenario. I bought a car with a single filament bulb in the socket, rather than a double (brakes and parking lights). When I stepped on the brakes, all the lights on the dash lit up a bit. Rough up the ground area and use some electrical grease to make a better connection. It sounds like this may be the culprit.
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Old 06-16-2008, 11:59 AM   #11
#522
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I checked the trailer connector, it's fine. I cleaned up the ground in the trunk, and checked continuity with a meter from that ground to various points along the ground wire in the trunk and at the bulbs and it tests fine. Also, the blinkers and license plate lights share this ground and they operate fine.

Looks like it is further up the wires. They run up along the passenger side of the car and bundle in with other stuff along the way and plug into a large connector just in front of the front passenger door. I will see if I can isolate it to being along there somewhere or on the other side of the plug, toward the dash side of the circuit.

Thanks again guys.
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Old 06-16-2008, 12:33 PM   #12
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After pulling the connector apart and if you can find the wire that goes to the middle brake light, or all the brake lights, see if you have voltage on the contact. If you do, then the trouble is futher up the circuit, but I think you may know that. I suppose another thing you could do is supply power to the light side of the connection and see what happens. All three brake lights should turn on but the trouble may be on the downstream side of the connector which I suspect it is.
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Old 06-17-2008, 09:15 PM   #13
#522
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Well, I unplugged all the connectors on each side of the car that are right in front of the doors and the 3rd light still comes on. judging by that, and the only reference to a connector in the wiring diagram is all the way under the dash, there is no connector anywhere else in line so I need to get under the dash. BOO.

This is pretty annoying esp since it's 105+ outside everyday. Today is a special 112 at my house...
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Old 06-18-2008, 10:51 PM   #14
Cougar4
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You might try pulling the turn signal flasher unit and see if the middle brake light goes out then.
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Old 06-19-2008, 03:05 PM   #15
#522
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OK, Fixed it.

I went back to where I started, the trunk. I pulled all three bulbs along with their harnesses out of the car and used a battery to test them by making contact at the connector. I touch + and - on the plug for the reverse and signal and they light up. I do the same for the combo bulbs (brake/tail) and nothing. I touch the + to one of the power pins, and then the - to the side of the bulb, and it lights up. Turns out, the ground wire right at the bulb was bad, on both sides. I just happened to make contact the first time I checked while they were in the car.

Just a word of advice, the ground on the bulbs back there is pretty lame. It's pretty much just wedged between the metal bulb socket and the plastic holder, not even soldered like the power wires are on the bottom.

I fixed it and all is well now. Thanks for the help guys.
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Old 06-19-2008, 04:25 PM   #16
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Thanks for the update.
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Old 06-21-2008, 11:01 PM   #17
ultrasonic
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Quote:
Originally Posted by #522 View Post
Stereo clock dims when pressing brake pedal
Interesting... I've had this symptom on my 91 Legacy turbo since I bought it four years ago.

I think I'll have a look in the trunk!
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