Temp light on

discovery 300 tdi 1998 auto (the mule)
Good evening , I’ve had a red transmission warning light come on and stay on , after wading through some deep water to get out of the village , ( yes still 3 weeks later )
Now I replaced the pipes last year and filter an after market oil cooler ( slightly bigger wit( a fan
The oil wasn’t hot
I’d only driven 2 mins
Even day after light is on , I’ve pulled the connector off fir now
Any help greatly appreciated

Replace the temperature switch

I will do this tommorow , I just found it odd that it was last year ,

tank you