Mark,
Your coach uses a DUVAC alternator (probably 160 amp Leese Neville), and the voltage regulator is built into the alternator. However, because the alternator output is ran through a battery isolator, the regulator depends on the sense wire to determine the proper charging voltage. Therefore, before you condemn the voltage regulator, thoroughly diagnose the system, especially the sense wire for the proper voltage and connection at the alternator.\
Gerald