diy bicycle auto led switch

having a trouble of forgetting 
to turn on or off your bicycle tail light?

well no more just build an automatic
 powering switch for the light whenever you riding 

for start i had a led shower-head 

that i got from my father that switches 
colors according to the water temperature
throughout a thermistor (resistor who change
 its resistance according to the temp)       

so i needed to hack the thermistor (temperature sensor) 
in order to control the different led colors
 (blue, green, red)  
to do so i used a 22kohm variable resistor
 for checking the resistance of each color
and then i could control the led with simple resistor

the last one was blinking red which was a great thing 
as it save me the use of another component 

so i just needed to hook it to a battery and a switch 
and figure a way to mount it to the seat 

the end result