subwoofer feedback help

[Garrett Tait 5]

ok so my buddy has a mazda6 with the bose system. he wanted me to help him out with his install. he found a diy for the car. basically what we did was take the signal from the factory subwoofer in the rear spare tire well and hooked that up to some rca's for the signal. the factory plug had 4 wires, 2 for signal, 1 for power (remote) and 1 for ground. i chopped the rca cables like the diy said and i soldered the wires behind the shielding to the designated wires. when we hooked up the rcas to the amp it worked and we were stoked, but when he turned the car on, there was a slight humming in the subs. i turned up the lpf and it was playing higher frequencies too.

 

whenever his car is off it doesnt hum. even when the stereo is off and the car is on it will hum. we did hook up another pair of rca's to my amps output and ran my signal to his amps inputs and it worked flawlessly. does that eliminate the possibility of a bad ground? ground loop isolator might not even work because the ground is okay because it didnt have the humming when we used my signal?

 

sometimes out of nowhere the subs will boom uncontrollably very loud to the point where it looks like theyre moving dangerously too much

 

 

 

not trying to sound like a noob but im really kinda embarrassed i couldnt help my buddy out when i couldnt understand what was going on

 

 

help please!

 

 

[Quentin Jarrell 671]

how exactly were the rca wires attached and what wires from the rca went to which wires on the factory harness.

 

how much voltage is coming out of the factory harness

[Garrett Tait 5]

the factory harness plugged into the subwoofer+amp which sat in the spare tire. i chopped that and soldered the correct wires to the rca's. i cut the rca cables and went to the center wire, which was covered in a foil material. i soldered and heat shrank those together. i also attached the power to the remote wire on that same harness.

 

didnt think to check the voltage of the wires because we were just following the diy. i had the gain up to about "0.5" to where the woofer was acting as it should (i checked/compared it on low volume in my car)

Edited June 9, 2013 by gt58

[Quentin Jarrell 671]

so if i understand correctly you have the center of the rca hooked up and not the outer wire?  RCA's have two wires in them.  The center which the positive and the outer wiring which is the negative.

[gprestonmoto 89]

I have a Mazda 3 with BOSE as well and if it's the same there's an amp under the passenger seat. The stock subwoofer plastic housing has a cap on it. You might want to grab feed from before the amp.