The TSAL indicates high voltage on the vehicle side of the AIRs. The circuit has 5 inputs in total, the AIR + coil, B+ and B- Capacitors of motor controller, AIR+ and AIR- contacts. The circuit uses a combination of logic gates, to achieve the required truth table.

A voltage divider, which is a combination of resistors, is used to step down the high voltage coming from AIRs and DC link capacitors. The circuit uses an opto-isolator to isolate the HV and LV on the same board. It also uses a 12V DC-DC convertor to isolate the grounds of HV and LV components. The output of the logic gates then goes to a comparator, which will pull up the value once the input voltage matches the reference.

The output lines control the Vcc of the LEDs, and they are grounded to the chassis. The blinking red condition of the LEDs is controlled by a IC555 timer circuit, using a set of resistors and a capacitor to control the frequency. The TSAL mount is a PLA 3-D printed assembly. It was chosen to reduce weight and achieve flexibility in design.