The Vanguard TSB can be used with a Vanguard ATRT-03 or TRF series turns ratio tester to perform transformer turns ratio tests using the same cable set provided with the TRM-203/403. Using the TSB, there is no need to connect and reconnect cables from the transformer after the initial connections are made. The user can conveniently perform resistance tests using the TRM-203/403 and turns ratio tests using an ATRT-03 or TRF instrument without having to make trips to the transformer to connect and disconnect cables.