Brand New Heavy Duty Automatic Glow Plug Controller for all 85-95 H1 non-turbo Hummers. This controller has 4 pins on the harness connector.
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.