On/Off Switch to thermostat sensor?? Can it Be Done...

Hi I have a problem I’m trying to solve. My car has trouble starting. Ive sent it in a few different times to the point I’m not willing to spend more money on it. I have figured away around it by plugging out my thermostat sensor the car heats up for longer and starts first time. My question is how would I break the circuit just before the sensor with an on/off switch to save me going under the bonnet to plug it out.