Car amp not working after car hooked up

[Marashz]

I am trying to wire in a car amplifier and there is already an aftermarket head unit installed with cables running back towards the trunk. Everything is assumed to be working at this point in time. BUT when I wired a positive and negative wire(s) directly from battery, the power light does not light up on my amplifier. Unless I unplug the car and have just the amplifier hooked up. Putting the ground against the cars frame doesn't do any justice either.

Anyone with any electrical knowledge please help me. I do not understand how this could not function. Unless my new amplifier and old amplifier are both shot out of complete coincidence.

Best regards

[StRaNgEdAyS]

The amp should have a terminal marked remote.
This is what switches the amp on or off as the head unit is.


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[geargrinder]

Yep. There will be a remote turn-on signal from the headunit normally.

The factory turn-on wire is a little all white no stripe guy. This will turn the amp on / off w/ the car from your aftermarket HU. You'd normally hook the remote-amp-turn-on out from the HU to that white wire, then be sure you're using that same white wire to turn the amp on in the back. Most of the "aftermarket HU to OEM wiring harness" adapters (Scosche or Metra or whatever) should do that automatically for you using standard color codes (I want to say remote turn on is blue or blue w/ white in 'generic car audio' but don't hold me to it...)

That is NOT and will not support the full power for the amp, you supply it with the actual power separately, either using the BMW factory amp power wire (red w/ green stripe IIRC) or by running a special dedicated wire yourself from the fuse panel by the battery. There's some nice big beefy unused factory fuses in that fuse panel (the "high current" fuse panel that is, behind the white plastic cover above the battery, not the little blade fuses) which make for a really nice tidy and 'factoryesque' way to add amps in.

[JimLev]

On a non DSP amp the amp turn on wire is white, it's on pin 2 of the 12 pin connector.

Amp2.JPG

[geargrinder]

Same on DSP...

[Marashz]

I totally forgot that I had posted this... but thanks so much for the help. It was in fact the remote turn on wire. The remote wire must have become disconnect behind the head unit. So I wired a jumper from the positive to the remote on the amplifier. All works great.. just fear of dead battery inc. I will wire a switch up to the cab once the weather clears here in NY.