On many GM powertrains the ECM controls the alternator’s voltage output setpoint. GM calls this is “Remote Voltage Control” or RVC. For a swap or repower situation this can present a problem because without other modules to tell the ECM what to set the output voltage at a RVC alternator will run in a “limp home” mode where it poorly regulates to ~13.5 volts, if it works at all. Under large loads the output in limp mode may drop under 12 volts.
These RVC alternators are easily identified as they have a 2-pin harness connector on the regulator instead of the older 4-pin. Most 58x powertrains sourced from salvage yards come with a 2-pin RVC alternator – usually a 145A or 160A Delco DR44G, sometimes a Bosch. Often they are replaced with a 4-pin regulator alternator to have proper charging.
The Tap-N-Cruise solves this problem and makes these otherwise excellent alternators perfectly usable in a powertrain swap or retrofit. It can command the voltage regulator setpoint between 12.5 and 14.5 volts in .5v steps. If you are using an OEM powertrain wiring harness with a RVC equipped powetrain no changes are required to keep the RVC alternator.