Coolant Temp Sensor more than one?

Hi all, I'm hoping as a complete newbie someone can help! We've got a 53 plate T5 1.9 T28 with a temperature coolant warning light on! We've changed what we thought was the only sensor on the bottom of rad, but light is still on. After a bit of research we are now thinking there's another sensor well hidden & fiddly to get too RH side of head? Also we bought the one sensor from gsf (brass ended 2 pin I think) but now found there's a four pin listed on gsf but not on other part suppliers? Just trying to go through a process of elimination with the warning light! It's not over heating and no coolant loss. The temp needle goes up to around 90 then drops. Any help would be greatly appreciated!
Thanks in advance

Thank you! We thought this was the case really appreciate the reply

Edited by Muddlingthrough - 03 Feb 18 at 15:59

I'm not sure.  Your best bet is to take it out to be sure because sometimes they are colour coded as well.  

Actually don't take it right out yet, just check which one it is.  That way you can just do a quick swap without loosing much coolant. 

Yes it's definitely worth replacing the O ring.  The sensor on the radiator isn't for the cooling fan as I said earlier, it's a sensor for the outlet temp on the radiator.  And it's a G83 rather than G62.  I presume the fans are switched by the ECU via a large fan control unit like the 2.5's are.