FC Fuel Sending unit
 

I am thinking that all the FC sending units are the same but can some one tell me different?

They are the same. I recently replaced mine. I had to first be sure by checking both FSM's for S4/S5 so it wouldn't matter which one I bought.

I did notice that the tops of the gas tanks are different.
the S4 tanks have a connector already wired to it,The s5 has a Connector that connects on the top of the tank and then runs a patch connector that in turn connects with another connector in front of the Rear wheel well,drivers side area.

thanks, helping a friend and gave him part knowing it would work but wanted to be sure as its been sometime since I messed with an fc

Actually, not exactly. The S4 and somewhat different than the S5's. The S4's have smaller/ more shallow gas tanks, so the mounting stalk and more specifically the length of the arm holding the float is a bit shorter on the S4's. Also, as I recall, the way you connect the sending unit to the underside of the lid is different on a S4 vs S5.

correct all S4 are the same and all S5.
I was speaking on S5 but your correct. Even mazda list a different part number on them.
Chad

Hmm, I stand corrected then :)
I did figure them to be the same because I checked the resistances per the FSM's. Hmmm...