HDIFix my Overheating 1991 ESCORT 1.9?

The relay is said to be constantly in the 'ON' position thus when engine heats up(traffic etc),no signal is being sent to fan to turn on.The thermostat is new,the wiring from the relay to the fan is AOK,the fuse is ok,and a 2nd relay was installed,knowing it was also working properly,and still same condition.The sensor was ruled out as not being the problem by the mechanic.HA!When the temperature gauge rose to 'L' on 'normal',only then did the fan come on.Mechanic thought there was a secondary relay,but couldn't find one.Summer is coming and I can't driver this Eccort with 77km in the HEAT.