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Old 02-17-2017, 01:51 PM   #1
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Aftermarket AMP in trunk, ALWAYS powered on


My friend has an E90 335i that had an aftermarket amp installed prior to him buying the car.

Lately he has been experiencing a strong battery drain and determined that the aftermarket AMP is ALWAYS powered on! Any advice on how to make it so it switches off with the car?

I told him it sounds like it was directly wired to the battery, and it seems like it needs to be wired to an accessory so it goes out when the car powers down.

Any ideas on what to check or where to look other than the main wiring for the power on the amp?

He also said this: "it was already connected to the battery when the previous owner had a stereo system installed on BMWs dime when they mismanufactured the car and didn't do the logic 7 stereo system
so my buddy eric just kept the same wiring in place when i had to replace the amp a few years ago"

So it sounds like the old aftermarket amp **** the bed and he had to replace it with another amp, but did not touch the wiring.
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Old 02-17-2017, 01:59 PM   #2
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It needs a signal from the Head unit to turn on and off, or you could just connect a cable from the tail lights, the amp only need's a signal not a whole lot of power.
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Old 02-17-2017, 02:20 PM   #3
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More information here, looks like it was all Alpine reference components and JL Audio amp 75W x 4. Installed in the car prior to his purchasing it for .... $4000!!!! dang.

I think something may have happened when his friend Eric helped him replace the blown JL amp with a new one. Stock amp is still in the car, but the new amp is up underneath the back window sill and all speakers wired to it up there.
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Old 02-18-2017, 09:46 AM   #4
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Is the Alpine amp mounted right side up? Or is it mounted up side down?

Check the wiring. As noted the amp gets power at all times but it needs a "turn on" signal (12VDC) from the head unit to operate.
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Old 02-18-2017, 10:55 AM   #5
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Hook up the remote wire to the headunit. It will turn on and off with the car. Only have the power in wire hooked directly to the battery

Last edited by Cayne23; 02-18-2017 at 11:42 AM.
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Old 02-22-2017, 07:03 PM   #6
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Turns out he's just slow. He sat and watched the amp and it shut down a minute or two after turning off the car. Why the delay?

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