Unit is used in an airplane tug to control forward and reverse in addition to speed through an electric twist-type throttle, similar to motorcycle. A multi-meter was used to test circuit integrity from two 12 volt batteries connected in series. Power was available to on/off switch and to forward/reverse switch. Power was also available at 24V to the controller mollusk connector. After re-assembling switches and reconnecting mollusk connector to controller, click of relay was no longer heard with activation of power switch. Prior to troubleshooting described above, the tug would intermittently cease movement, but relay click could still be heard, and tug movement would eventually be possible, sometimes after a few minutes of waiting.