i have gone through the exactly 100% same problem like your.. with my charade g-11
i wasted money on two of these pumps..
actually i used 3 of them but the first on was original mistubishi and it served me for 6 years.. in this you can see there is a mechanical system to turn it ON and OFF repeatedly, but in mistubishi pump there was small circuit board for this purpose...so that on was really realiable.
i will sugest you got for that...on the bottom of that you can see the circuit board..
if you failed to find original one, go this sir xulfiqar's suggestion...and you will be tension free for the entire life of your car..."only if done correctly"