gearbox warning light

hi all hope someone can help got 300 tdi auto towed caravan this weekend about 8 miles into journey gearbox oil temp light came on so stopped and felt oil cooler witch was hot as was pipes going to it had a fag them felt them a cain and they were stone cold so set of again about a mile later light came on again with pipes and fan hot but after 5 -10 mins stone cold any thoughts cheers andy

hi all changed gearbox oil filter cleaned oil pipes and cooler today still no different could someone please help before truck go s on ebay cheers andy

does t/c lock up .was oil blackish if yes to first and no to second fit new switch or remove wires

tc does lock up oil gearbox oil was red almost clear and thin like water

wouldnt worry then pull wires of switch