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Discussion Starter · #1 ·
I started seeing a strange issue in my car. The HU unit power cycles intermittently when brake pedal is tapped. First this happened only occasionally when car was in park, but today this happened on a road too. Moreover, I noticed that instrument cluster lights dim when I tap the brake pedal. What's going on? Time to replace something?
 

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Discussion Starter · #2 ·
I just realized that it's not only the brake light that's causing some of these things. For example, pressing the rear window defrost button makes the dash lights dim a little for a moment. It almost feels like the car is struggling to power everything at once. As you turn an additional device, voltage temporarily drops for other devices for a moment. I could be wrong. Could this be alternator or battery issue? Or maybe some cables? Note that lights dim and stereo goes off when brake pedal is pressed when the engine is off, so I suspect it's not alternator. If not alternator, then what?
 

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I would suspect your battery is at the end of it's life. Go get a free charging system check at Autozone or Advance or somewhere. If the stereo is going out when the car is off and you press the pedal I'd do it sooner rather than later.
 

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Discussion Starter · #4 ·
I'll do the check, but it's really odd that stereo now goes off just as frequently with the engine on, sometimes on the road! Shouldn't alternator be powering things when car is moving? I really hope that only my battery is going bad, and not alternator.. maybe it's time to think about the big 3 upgrade too.
 

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Clean & tighten all battery & alternator connections, too in addition to the load tests. Unfortunately the alternator on the Duratec is very hard to access.
 

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Discussion Starter · #6 ·
Wal-mart crew measured the battery to have 570 cranking amps. The battery rating is 610 amps. They advised against changing the battery. So, if it's not battery what should I test next? I suspect the the problem is neither the battery nor alternator. This issue happens with engine on or off..
 

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You need to test the voltage under load. But it is low because the lights are dimming.

A bad battery unless it is shorted out will never cause the problems you are experiencing. The problem is the alternator cannot produce enough current at the rpms and load you are at when the lights dim.

OR the wiring is deficient and will not let the full current flow. This could be due to corrosion or mechanical damage if you have not added large electrical loads.
 

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Discussion Starter · #8 ·
The way I see it, since I am seeing these things with the engine either on or off, I suspect it's neither battery nor alternator problem. Moreover, while my battery terminals are not the best ever, they're reasonably clean. I clean them and apply some spray that's supposed to keep them clean..

I suspect the problem is somewhere with wire contacts, or wires or fuses or lamps. I will check these things later. I suspect the brake light cable is just shorting somewhere causing other things go bezerk. Also, I want to see the ignition on wire, the one that lets the stereo to turn on when key is turned.

BTW, I also have a new ~500watt (RMS) amp in my trunk, so it's turned on when the stereo is on. It's been working for at least a month without issues.
 

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start checking the grounds especially the one by the battery.
 

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I wonder if there is a short in the brake circuit. Try hooking a clamp meter (or a multi-meter) to the battery to read the amperage flowing in the circuit. Then depress the brake pedal and see if the is an unusually large draw of current when the pedal is depressed. That might help you narrow down the problem. Current flow should be less than 1 amp before you push the pedal.
 

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Discussion Starter · #11 ·
You need to test the voltage under load. But it is low because the lights are dimming.

A bad battery unless it is shorted out will never cause the problems you are experiencing. The problem is the alternator cannot produce enough current at the rpms and load you are at when the lights dim.

OR the wiring is deficient and will not let the full current flow. This could be due to corrosion or mechanical damage if you have not added large electrical loads.
I added a 5-channel amplifier recently but it's been working fine for months. Moreover, strange things happen when it's off too. For example, the dome light blinks for a split second when I tap the brake pedal..
 

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Discussion Starter · #12 ·
Ok, so today, I cleaned the battery and battery connector terminals, which were a little rusted. After doing this, the receiver still resets after I press the brake pedal. Next, I checked the stop light fuses and the lamps. All were ok. After that I took out the head unit's fuse and the connector, and then plugged them back. It stopped resetting once I press the brake pedal after this. It's really strange. I hope things will keep on working from now on.
 
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