Alpine MRV-F545 not powering sub. What am I doing wrong?

[ryz0n]

Well, I'm supposed to bridge channels 3 and 4 on this amp to run my subwoofer, but no matter what I've done, the sub has not been powered once. I'm thinking either i'm not connecting the RCA's correctly, or there's something wrong with the amp.

Amp is CH 3/4 Filter LP setting, x1, input channel 1+3, 2+4. I also tried on 3/4 too.
I have 4 RCA's on my head unit, F+R plugged into front, F+R plugged into SW(subwoofer), nothing plugged into R(rear). Where should the RCA's be plugged into the amp, and do I have to switch any of the plugs in the HU?

[KU40]

what is F+R RCAs plugged into front, F+R plugged into SW? Do you mean Left and Right? The RCAs for the sub should be plugged into the subwoofer output.

Does the amp turn on?

Is there a setting on the head unit to turn on the subwoofer output?

The RCAs on the amp should be plugged into the two channels you are bridging for the sub. Since you are doing channels 3 and 4, you should be plugging them into the middle two RCA jacks on the amp there.

[nismo]

Your subwoofer output from your deck goes into channels 3 and 4. It is the center set of RCA's on your amps.

Eric