To me anyways looks like a bi-metal turn signal/flasher plug in component. Those would get hot when the 2 metal contact points heat up to separate and open circuit. Can go defective of course and/or be out of calibration.
Out of the Navy my first job in electrical field; used to repair and cal the machines that tested those at Sylvania; dead end job but a transition, forgot all about that.
3 terminal, seems would be 12VDC pos & neg to heat bi-metals parting contacts and other terminal to be switched on and off.