Almost certainly the hazard switch itself, although it could be the combination switch.
The switch can be disassembled by carefully prying the top and bottom apart where the catches hook over each other. Careful! Watch for flying bits and where the bits come from. Once you have it apart, you will probably find the spring contacts have lost their tension and can be carefully bent to give good contact. 
You can also check continuity - unplug the switch and check from the circuit diagram which connection is which and check continuity in both psitions.
John
				
			 
			
		 
			
				
			
			
				John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
			
			
		 
	
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