Yesterday he checked the ground connections and that was all ok and then he disconnected the RH alternator voltage reg from the LH voltage reg and guess what ? The LH side is working like advertised , holding 27.5-28 volts output and as rpm increasing the VR was sending between 11 to 15 volts to the alternator field depending on rpm so the problem is on the RH side.
Same test with the RH side showed 31 volts , suspect there is unregulated 28 volts somehow getting to the RH alternator field circuit but the connection is not at the alternator. Probably a further incorrect connection somewhere within the bowels of the airframe.
To be continued ....