Matt, with this diagram you would not have any sound to the rear speakers because there is no RCA connected to the rear jack on the bottom amp.
I could be wrong but I believe that when the 4 or 2 channel switch that has been labeled as 2 channel by zlek131 in his drawing it would allow just 2 RCA's to be used on either the front or rear input and drive all 4 channels of the amp. Basically I think that switch just jumpers the right rear input to the right front and then the left rear input to the left front input. It's been a while since I worked with Rockford but I just did a Pioneer amp today and that one had a 2/4 channel input switch.
Thank you Jim and Steiner! I really like the idea of using the y-cable. I assume that will require 2 y-cables, one to split the rear "red" RCA out and one to split the rear "white" RCA out, correct? Does it matter if I use the Y-cable on front or rear RCA outs? Above I mentioned rear but is there an advantage one over the other? I like the idea of being able to control/adjust the subs via a remote. The manual says the remote is optional so I assume I can buy one. I'll redraw my wiring diagram for final approval.
Also for power here are my plans. I pre-wired everything when I had the inside of the car apart last winter. I have a nice thick/red 4 gauge wire running from junction box (front behind the battery) to the trunk. This wire is fused about 8-12 inches from the junction box. Per Jim, I’ll plan to split that off to each amp and then fuse each branch so each amp will have its own in line fuse. I should be good to go with my battery’s negative terminal as I redid my battery terminals not too long ago and have a very good ground to the motor and frame. See pic below. I will also plan to ground each amp via a 4 gauge wire directly to some portion of the trunk. Can I ground both amps to the same spot in the trunk? I also pre-wired my “blue” wire to turn on/off the amps and plan on splitting it off to each amp.
Pic of my ground terminal (1/0 welding cable) coming of the battery to the block and then to the frame.
No problem for the help.
Yes, you would need two RCA "Y" cables but sometimes the cable is not long enough to reach each amp so you may take some measurements to where when you go shopping you will get the right ones.
As far as the cabling you have run, unless the frame is tied into welded in frame connectors and the welded to the body of the car, most times grounding the frame doesn't do anything BUT it doesn't hurt. You do need a ground from either the engine block or the battery negative terminal to the body of the car unless how you have it with the frame grounded AND you have welded in frame connectors to the front frame and then welded to the floor pan. Most subframes are floating on rubber bushings under the car and also at the radiator support.
Hopefully the wires you have run are a copper wire. I would think 4 gauge would be sufficient for both of those amps BUT if it's a 4 gauge copper clad aluminum wire (CCA) or aluminum wire, then it probably won't be large enough. A lot of shops sell a cheaper 4 gauge wire but there is a reason for this. 4 gauge copper can handle more power than 4 gauge CCA wire. 4 gauge CCA wire is less expensive than 4 gauge copper wire because it is over 90% aluminum. To put in place CCA wire instead of copper wire requires from what I've read, 1 to 2 larger wire sizes so if something needs 4 gauge copper wire and you then substituted CCA wire then the wire would need to be a 2 gauge or larger.
If you do get the Rockford Bass level controller, make sure it is made for the amps you have. I think they did a design change a while back and the new controllers do not work with the older amps and visa/versa.
You can ground the amps to one point but clean the area down to bare metal and try to make a nut and bolt connection and not self tapping screws or regular sheet metal screws. Depending how thorough you want to be add a star washer or two and then after the connection is tight, cover it all over with a black silicone caulk. If needed later the caulk can be removed but it also helps seal the connection.
As 67Rally said they do make fuse distribution blocks BUT do not install whatever fuse you want but use the size that Rockford says to use for those amplifiers. Even though a fuse holder may hold a 200A fuse, you do not put that size in unless it is needed.