1. Remove the 6-pin plug from the heating control relay, turn the ignition key to position "2" and connect the control wire chips 1 and 3 on the plug.
2. If now the heating control lamp is on, then the heating control relay is faulty, replace the relay. Otherwise, remove the bulb, check it and replace if necessary.
3. If the lamp is in good condition, then check with an ohmmeter the passage of current through the black wire between chip 3 and the incandescent lamp, if necessary, check the contact of the lamp with the body, eliminate the wire break.
Attention! If the preheat lamp stays on for a long time, this indicates a malfunction of the preheat control relay (contacts stuck together).