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before i begin, i would like to thank you in advance because i know someone will eventually help me with this.

so i have the alpine 9884 headunit. the subwoofer preout does not work, there is no signal. i tried different rca cables. the "fronts" preout works but the subwoofer preout does not. the amp works because it powered the front speakers. tried different settings on the amp but still nothing. everything is ground and installed properly.

i am lost at this point. what do you guys think? could it just be a bad head unit? it's brand new. also, i dont have the remote wire connected to the head unit. could that be the problem? the remote wire for the amp is connected to some other wire underneath the steering wheel. i had the amp and a sub installed a year ago paired with the stock headunit by some audio place. hence why there is a new headunit.

please help, thank you.

 
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ok just an update, i purchased a new HU to see if that was the problem but still the front rcas work and SW rca does not. tried different cables and settings but still nothing.

 
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are you sure the SW-out is even turned on from the deck? go into options and make sure. i know alpine has alot of options to turn on and off external and internal amps. if anything, you should do a hard reset once everything is connected by pushing that small button in with a paperclip. its usually on the radio itself behind the faceplate. that will reset all the settings to factory.

okay if you tried a new hu, somethings wrong with the amp then or the way you wired it. check all your connections, make sure the amp is getting power and that the sub is properly hooked up with corect ohm load, etc.

 
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so i just triple checked everything. the amp works fine: it works with the inverter input and also the rca input from the HU for the fronts. checked the fuse and it has power. the sub is hooked up correctly because it still works with the inverter input that was previously installed a year ago.

the only thing i am not sure about is if the SW-out is turned on. the god damn instructions suck. but when i go into subwoofer level, i am able to change it from +0 to +15 but still nothing.
UPDATE: just checked to see if SW out is turned on and it is.

 
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another update

so i got a new 4 channel amp. the fronts work but the sub still does not work. so i tried the inverter input and that worked with the sub. very odd.