An electronic device for simulating load currents when testing a tow-vehicle brake controller is described. The electronic device utilizes current monitoring circuitry to measure a current of an input signal from the tow vehicle. The electronic device also includes a series of resistors that are arranged in parallel on the input signal as wells a series of switches (e.g., relays or transistors) that can activate and deactivate each one of the resistors. Microcontroller circuitry within the electronic device controls the series of switches based on the measured current of the input signal, and, by extension, controls the series of resistors applied to the input signal. In so doing, the electronic device is able to simulate a desired load current on the tow-vehicle brake controller being tested.