Brand New Heavy Duty Automatic Glow Plug Controller for all 1992-1993 C/K pick-up's, Suburbans and G/P Vans and cab/chassis trucks (school buses), and 85-95 H1 non-turbo Hummers.

This controller is what turns your glow plugs on and off by a signal from the coolant temp switch.  Replace when glow plugs are not operating properly. I recommend replacing every time to plugs are replaced as preventative maintenance or every 100K miles.