Abstract: The disclosure includes improvements in the field of retrofit-detector installation such as adapters that simplify retrofit of addressable detectors onto previously installed zone-type system hardware. Each adapter includes electrical circuitry for electrically connecting new addressable detectors with legacy system once installation is complete. The disclosure includes structures that permit users to efficiently solve a number of problems that may arise during installation of retrofit-detectors into legacy systems. For example, one or more switches may be used to reverse electrical polarity to thereby correct polarity and/or mapping faults. One or more switches may also be provided to disconnect at least one electrical terminal to assist in locating ground faults and/or other wiring problems. One or more test points may also be provided to test one or more electrical characteristics relevant to retrofit installations.