The VX4236 and VX4237 are single-channel DMMs, with only channel A activated. You must connect to channel A (pins 1 through 8 of J351) shown on page 1-6 of the VX4236/VX4237 User Manual. The terminology for the DMM inputs: Hi, Lo, I+, I-, and Guard came from DMM Metrology equipment. The DMM Hi, Lo inputs are used for all AC / DC Volts and 2 wire Ohms measurements where the Lo DMM input is usually connected to circuit ground side for proper polarity reference. Shown below is a VX4237 DMM, typical Scanner application used to measure the resistance of or a voltage drop across Rx. The DMM +I, -I inputs are used for AC / DC Current measurements where the -I DMM input is usually connected to circuit ground side for proper polarity reference. Shown below is a VX4237 DMM, typical Scanner application used to measure the DC current flowing through Rx. The VX4237 Hi, Lo, +I, and -I inputs are used for 4 wire Ohms measurements. Shown below is a VX4237 DMM, typical Scanner application used to measure the resistance of Rx.