Have had a reoccurring engine light coming on after full throttle /full speed pulls after more than 15-20 seconds. One symptom is the fan not switching on when the temp sensor and thermostat have both been replaced. The second thing which is now occurring on the heads up display is my RPM is completely out of whack. RPMs are now showing in the minuses, like -21 to the -2500 and higher which is now (seems to be) permanent thing my heads up is now monitoring. I’m now thinking the engine light is turning on because it sees this abnormal RPM condition. The service manual says very little on the RPM monitoring circuit. The fan motor does kick on and cool the engine after several minutes eventually but seems to be hesitating to come on. Any ideas here ?