We are putting a LS3 into a Range Rover. Using a Speartech standalone simple loom which controls the engine cooling fan through J1 58. Now the engine starts cold and runs for 20 seconds and the engine cooling fan kicks in and stays on. We can control the trigger to the fan relay in EFI live so I know the wiring to the fans is correct.

I have tried many settings and have been persevering with the issue for about 4 weeks and now have 4 conversions with the same issue.
L76 - 6L80
LS3 - TR6060
LS3 - 6L80
LS3 - 6L80

Water temperatures are reading correctly
IAT correct
Engine runs fine

Possibly to do with air conditioning. Not sure if not having any of the air conditioning wired in at all is making the E38 go into some sort of cooling warning over load.

Would love to know if anyone retrofitting engines into odd vehicles have come across this issue before.