On that defrost control board, the troubleshooting that you are describing indicates that you need to check for 24 volts between the Red and Black wires (marked on the wiring diagram below). You will also need to check for 24 volts between Yellow and Black (also marked). If the control board is getting power and the LED light is not on, then you probably have a bad control board. If you are not getting power, then you could have a bad power supply or a wiring failure. I do not recommend that you conduct that live voltage check unless you are completely confident in your technical ability so safely measure it using a volt/ohm meter. Disconnect electrical power as soon as the voltage check is completed. The other troubleshooting step involves using an INSULATED jumper wire to short across the connection marked DFC_DFT on the control board to a pin marked TEST_COMMON. I don't recommend that you conduct that test yourself. A service technician will need to perform that check. These additional tips may help. If you need more assistance, reply with additional details.