How many total speakers do you have? The CR-814 will run 2 (usually dash, low -wattage channels)direct from the head, plus whatever number of channels the amp(s) will handle. The typical amp with the CR-814 was a 4-channel, usually a 4 x 20, part number 3533004, or a 4 x 40 found in the 960s. However, if the vehicle came with rear deck speakers as well as dash an all four doors, the rear door and rear deck speakers on either side may be on the same channel, but are 8-OHM WIRED IN PARALLEL, not 4-ohm.
What additional amps did you buy, and how did you hook them up?
Better get the wiring diagrams AND physically verify that your wiring matches the diagrams before you go much farther.
Do you have an external fader control still hooked up for an original multiple-amp setup? The 814 has its own fader in the head unit as well. Is it possible that you have two faders working and that one is suppressing the rear output unknown to you?
Sorry I can't be much help, but I'm not all that familiar with the setup on the 780. If you were running multiple external amps, tho, it seems likely that there was an external fader and a splitter between the head unit and the amps. Check the faders first, including the setting on the 814 head unit; maybe there's an easy solution.
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We have met the enemy and they is us. [Pogo] S70 T5 cop car : Rough Rider suspension, Walmart fog lights, eBay speakers, ambiance by Pall Mall, trim by Le Duc d'Tape, 8-channel THD by OEM amps