Difficulties with Alpine MRD-F340 amp

I need some assistance from those that are familiar with how to setup an Alpine amplifier. My amp for my four door speakers is an Alpine MRV-F340 V12 series four channel amp. It is bridgable to two channels and puts out 55 watts RMS to four channels, or 90 watts into 2 channels at 4 ohms.

I considered bridging the two channels, so I ran speaker wire to the deck, connected it to the right and left front speakers, and ran my RCA's (my Pioneer head unit has a right/left RCA for each channel, front and back, for a total of 4 pre-out jacks. I connected the RCA's to the input jacks on the amp and fired it up. I only got sound from the right front speaker, nothing from the left. I faded the output and the results were not as expected. I moved the RCA's at the amp to different positions, and got different output, sometimes both speakers would have sound, but the fader was reversed, or wierder still the fader didn't make much difference, the right speaker would always be going, just not as powerful. I monkeyed with it for a while before giving up in frustration. The speaker connections at the deck are good, since I can get sound just fine, just not with the right settings. I'm sure my RCA connections are backwards or something....but who knows.

The other thing about the amp is has an "input selector" switch, that is labeled with three settings similar to "1+2/3+4", "3/4", "1/2". I read the instruction manual and it didn't make much sense as to what these are doing. The manual for this amp is sparse. Basically it sucks. I guess Alpine assumes everyone are experts at setting up their amps and don't need detailed information about the settings. I need some assistance.

Anyone have an idea what the settings need to be to bridge the amp? Do I need a Y connector for the RCA's? Anything else?

I do have two RCA's one for the front channels and one for the second channels. I wired the head unit RCA's so that channels 1 and 2 would be the front channels and 3 and 4 would be the rear, but I think the Alpine has that backwards. I'm thinking it is 1 and 2 for the rears and 3 and 4 for the fronts but that doesn't make much sense to me. Also, I know how to get it hooked up for four channel mode, my problem is getting it in 2 channel.  bridged correctly.

set the switch to 3&4 to have the inputs of ch3/4 accept independent input signal

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This model amp doesn't have the digital display or controls. The gain and the input switches are all manual screw type adjustments.