ground to the engine is good.
I'll try your suggestion on switching relays Vadim.
This isn't a new problem either. I had a bad MAF, which caused the ECU to go into limp mode and the fans ran non-stop. Then I replaced the MAF with a good one, found out the ECU was bad, got a new one of those, and ever since then, the fans haven't turned on when they are supposed to.
Which is why I thought it was the temp sensor incompatibility thing.
Just wanted to see what others think too.
Is there a way to find out what year your ecu is?