An electric motor of an electric submersible pump is electrically isolated from a power conduit for diagnostic testing of the power conduit and wet connection components in place within a wellbore. The electric motor is electrically connected to the power conduit through a wet connection assembly having motor leads in electrical connection with a transfer contact and a receptacle assembly disposed on a tubing string having a supply contact electrically connected to the power conduit. Electric power flows through the power conduit, through the supply contact, through the transfer contact, and through the motor leads to the motor. The supply contact and the transfer contact are separated by a sliding sleeve that hydraulically inserts between the contacts, insulating the transfer contact and grounding the supply contact for testing. The contacts may also be separated by a relative rotation of the assemblies that grounds the supply contact for testing.