Transmission Cooler runs (and runs and runs)

[Arcticdude]

I only have a limited bit of experience with 380’s, so take this for the guess that it is. I think the transmission cooler is oil to water, so it won’t have a fan beyond the engine fan. But, the hydraulic cooler will have fan(s) and should be located on the driver’s side. That being said, if I’m anywhere close at this point, your hydraulic oil tank will have a temp sensor screwed into it. It should have 2 wires (though it may only have one). Try disconnecting a wire. Does that stop the fan? If so, you probably have a bad temp sensor. The other possibility is a stuck relay. Find your fan relay and remove it, swapping it for a known good one.
I hope this helps.