The heater is usually the outer 2 connections on the display and will read 3 ohms or so, but you can if get a magnifying glass you can see the heater wires, they are nearest the glass above the numbers, when they fail the wire breaks, unless the connection goes bad.
Is there a choke or tranformer of any kind, its driver transistor is also a likely fail.
What does the display do, nothing?, or something weird.
How is the clock set, are there buttons built in, or are they somewhere else in the car?