Glow Plugs
Glow plugs are small 6-volt heaters operated by an electronic relay. They cycle on and off, powered by 12 volts to give rapid heating. Glow plug light on dash should glow as plugs cycle on and off.
If test light is connected to glow plugs and ground, it should flash on and off. Relay can be heard clicking on and off after ignition has been on for approximately 25 seconds.