Just curious if your newer ACE uses the Intellitec BIRD battery control system with the basic configuration shown below? If yes, you seem to have found the Coach battery latching relay and the 5 amp fuse, but there should be a BIRD control module, interconnect relay and Chassis battery latching relay somewhere (the BIRD basically controls the interconnect relay between Coach and Chassis battery). If your newer ACE does not use the BIRD system then it is more difficult to help. A basic multimeter would help you determine if components have failed. No noise from the coach latching relay implies it has failed (assuming its control wires and switch are working properly.
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