Thanks James. So if I am reading this properly, as the sensor is in circuit the whole time except for the moment I press the button, the ECU is receiving temperature sensing data and therefore sending the correct amount of fuel to the injectors.
if the switch " spikes the signal" (and switches spike when they close and open..) then the answer is no, if the ecu see`s that spike..
at the point a switch opens or closes.. there is a point where its neither fully closed or fully open but electricity can flow across the gap.. its partial because its not fully connected nor disconnected. its a high/ low resistance just at that point... and that changes the complete thing.. it becomes two things in union.. a resistance circuit in parallel and connected to the ecu..
if i wanted to turn the fans on or off.. i would use the fan direct feed... nothing that the ecu uses to sense.. i dont want to change anything the ecu can see.. i want to change what the fans do.
the easy solution.. isnt the easiest consequence,,
i think that using an ecu sensing circuit is the wrong way to influence turning the fans on or off... unless one is moving the sensor.. physically.. and so changing its environment.. ie if you move the sensor to a hotter place... it turns on sooner...
one needs to use an ecu output circuit... there - the ecu has already made its decision.. you just change that.. not what it senses before it makes its mind up//
you are not interested in the ecu making its mind up what to do... you want to change what it decides at any time before or after it decides... and not change its decision... just its consequence,, and that should not include the ecu.. you dont care what its decided. The ecu controls many things based on its decision.. but you just want to change one... and one only.. what fans are on or off when you press a switch.. that cannot change what the ecu can see... but changes its consequence.
THe ecu has decided the fans are off.. its also decided the air fuel ratio, and so determines the signals it sends..
you dont care about that... you are not altering what the ecu signals... you change what those signal do.. and in the case of the fans... you decide .. not the ecu.. if they are on.. or off. You dont care that the ecu thinks its cold.. or hot... and dont change what the ecu thinks.. it can carry on thinking what it wants... and so.. because you turn the fans on... it might see that the temp senor now can see something different.. the coolant is cooler... so it it changes the air fuel ratio... you dont care about that.. your choice was to make the fans run regardless of the ecu..