Adapters Model: SM-420 Adapter SM-420 The SM-420 adaptor has been designed to interface from any 4 to 20 milliamp tank sender unit to the Smart Switch Technologies HT-100 or HT-100/P Tank Control System. Wiring Diagram: To HT-100 or HT-100/P 4 to 20 Milliamp return -ve SM-420 ADAPTER Batt + Out (feed +ve) Tank Sender Unit Ground DC 1A FUSE + VDC Calibration: The tank calibration is preformed inside the HT-100 or HT-100/P therefore before starting ADJUST the tank sensor probe for the FULL 4 to 20 milliamp current swing. Calibration can now be done as per the manual for the TC-8000 or TM-4000 unit. HT-100 or HT-100/P 4-20 Milliamp Sender Unit Current Meter