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Thump noise when keying up


Michigan boarder

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I installed my stereo a few years ago and this was never really much of an issue but it's bothered me lately.  I have an Alpine 9856 HU, a Boston Acoustics GT40 amp, and an Infinity Basslink sub.  When I turn the radio on with the dash toggle switch it powers up normally, with or without the engine running.  But when I kill the engine with the key but not turn the radio off, and then start the engine back up the radio powers off and back on and makes a loud thump noise.  Is there a way to fix that?

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1 minute ago, 90oldskool said:

is the remote wire to the amp powered from the red wire or blue wire on head unit ? 

I cannot recall which color wire, but it is definitely to the wire that is for the remote power as labeled on the HU.  IIRC, I spliced that wire to the sub and to the amp.

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What is the power source for your dash switch?  Constant (B+) or switched (ignition)?  i.e. when the dash switch is on but the key is off does the stereo stay on? And if the stereo turns off, can you verify whether the amps are turning off and on?

Edited by shawndoggy
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2 minutes ago, shawndoggy said:

What is the power source for your dash switch?  Constant (B+) or switched (ignition)?  i.e. when the dash switch is on but the key is off does the stereo stay on? And if the stereo turns off, can you verify whether the amps are turning off and on?

The dash source is constant.  I can have the key out and in the glovebox and the dash switch will power up the stereo.  Amp is connected directly to the battery for positive (with an inline fuse) and negative.

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do you know where the wire powering the switch actually runs (did you pull the wire straight from the battery or....)?

Also how many batteries do you have?  What's the voltage when cranking?

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4 minutes ago, shawndoggy said:

do you know where the wire powering the switch actually runs (did you pull the wire straight from the battery or....)?

Also how many batteries do you have?  What's the voltage when cranking?

No idea on the wire source, I used the existing harness and it appeared to be the factory power supply.

1 battery.  Not sure on the voltage while cranking, are you thinking it is pulling too much juice and cutting the power to the radio?

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Just now, Michigan boarder said:

No idea on the wire source, I used the existing harness and it appeared to be the factory power supply.

1 battery.  Not sure on the voltage while cranking, are you thinking it is pulling too much juice and cutting the power to the radio?

Yes, or wherever your source wire actually terminates is doing it.  As a temporary experiment I would try repowering the switch right from your battery's positive post and see what happens. (<--- that right there is lazy man electrician work...).  If it still turns off and on it could be that when cranking the voltage is dropping below what is required for the stereo to stay on.

Edited by shawndoggy
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Just now, shawndoggy said:

Yes, or wherever your source wire actually terminates is doing it.  As a temporary experiment I would try repowering the switch right from your battery's positive post and see what happens. (<--- that right there is lazy man electrician work...).  If it still turns off and on it could be that when cranking the voltage is dropping below what is required for the stereo to stay on.

Thanks shawn, good idea. 

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1 hour ago, shawndoggy said:

Yes, or wherever your source wire actually terminates is doing it.  As a temporary experiment I would try repowering the switch right from your battery's positive post and see what happens. (<--- that right there is lazy man electrician work...).  If it still turns off and on it could be that when cranking the voltage is dropping below what is required for the stereo to stay on.

Make sure to use an inline fuse close to the battery on this power wire, even as a temporary "test"

cant tell you how many "test" I have rigged up and then left that way for months or years as an "I'll fix it later" job. Haha.

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