Fuel sender question

Another question from a complete Z novice

I am trying to connect a low fuel sender module to the bike. The original dash was destroyed so I fitted a single speedo with idiot lights. I seem to be confused. I thought there would have been some juice going to the sender but there isn't any. Can someone please explain to me how the whole circuit works?

What bike is it? Does it have an electronic low fuel switch or an electro-mechanical fuel gauge?

It has a float type sender. I've measured the resistance by moving the float and it's working, The bike is a Z750P1 (UK) Spectre (US) I think the yellow wire is the one that goes to the gauge and on these bikes there was an electronic LCD gauge which is destroyed. So what I need to do is rig up either another fuel gauge or some sort of thing which lights a LED when the sender is either at high or low resistance 9(low gas)