Yes, the fan always stays on. When i turn in the ignition key the fan is already kicking in.
So i looked at the wiring diagram, if i am reading it correctly, the wiring for tachometer goes into the ECT sensor and the temperature gauge goes in the ECU. How do i check the connections with multimeter ?
Sorry i am not mechanically inclined
That is definitely not right. The fan should only come on when the coolant temperature is about 103 Celsius.
Either there's some short circuit that's permanently engaging the fan relay or someone's done some dodgy wiring to compensate for the faulty coolant temperature reading.
The wiring for the tacho should go to the ECU not the ECT sensor.
1) Disconnect your battery (very important!!)
2) disconnect your cluster connector and ECU connectors.
3) put the multimeter in continuity buzz mode and probe from the relevant pin on the cluster side to the ecu side
E.g. if the tacho signal was pin 6 on the cluster and pin 36 on the ecu, you should probe those two pins. If the wiring is good, the multimeter will buzz and indicate a resistance of 1 ohm or less.
If the wiring is faulty it may indicate a higher resistance or complete open circuit with no buzzing.
To probe those type of connectors you may need to get some automotive type probes or use some connector wire. Ensure you get the right pins and in case of the ECU, the right connector as well or you may be chasing a problem that doesnt exist.
I dont have the schematics handy to tell you the pins/wire colour.