Radiator fan on permanantly

After a trip to the lakes this bank holiday the van has decided to never switch the fan off, even without the keys in the ignition. the only way I got to switch the fan off was to disconnect the battery. I've had a quick poke around but can't see anything suspicious.

Before I go have a serious poke I was just wondering if anybody has come across this before? or has any idea of where to look first.

Thankyou in advance

Which engine is yours and what year?

1.3 efi 1998

Fan switch which is in the coolant pipe closest to the passenger side, it's a bit of an arse to see but its there. Has an electrical connector, it's sort of under the coolant header tank.

Or it could be the rad fan relay. Which I think is under the passenger seat.

tbh, I think it must be the relay.