Preheater System, Check
Disconnect wiring plug connection for coolant temperature switch.
Connect voltmeter between sheathed glow plug and engine ground.
Set starter switch to position "II" without actuating starter. In this position, the preheater telltale must illuminate for approx. 3.5 seconds and the voltmeter indicate voltage supply for 7 seconds.
If there is a deviation, check wiring harness, relay and thermoswitch.
Connect wiring plug connection for coolant temperature switch.