To test a block heater with a test light, follow these steps:
1. Locate the block heater and unplug the electrical connector.
2. Connect the test light to a metal ground.
3. Touch the test light probe to the terminal inside the connector.
4. If the test light illuminates, the block heater is functioning properly.
5. If the light doesn't come on, there may be an issue with the heater or its wiring.