Sludge Pump question

Hi , I'm new to this forum.
In my house I have 2 bathrooms , 1 up & 1 down. Today my lower toilet would not flush, it would not drain. Usually I hear the sludge pump kit in.
I looked at the plug in the wall & there was 2 power cables coming from the sludge hole..down into where the pump is. One plug was plugged into the top of the other plug & plugged into 1 socket in the wall. Understand what I mean? 1 of the power plugs had a plug on top of it.
Anyway..the pump would not turn on. So I unplugged the one plug that was plugged on top of the other plug lol...and plugged it into the wall. Finally the pump came on & started pumping. But it seems like it didn't want to turn off. So I assume the second plug controls the auto float detector?
Thats the question...what is the second power plug for. If the pump will not work automatically..do I need a new pump ? Is a cast Iron pump better & more durable? How long do these last?
My other sump pump never lasts very long.
Thx