1990 Cadillac deville 4.5, tested radiator fan with alligator clips and they turn on and the fuse is good, changed the coolant temperature sensor, but they still won’t turn on when they should and I don’t want to keep overheating the engine
Could be a relay, or a wiring problem, almost anything on a car that old. I'd check the relay but if that's not it you need to obtain a wiring diagram and do some basic electrical troubleshooting to locate the fault.
Forget the wiring diagram.... because I'm about sure you daily drive it and use it for work and so on. Wire those fans straight....wire them to a toggle switch that way you can shut them off your self. Find some YouTube videos on it. I've done that a lot on these old cars and it will be fine....screw all the other hocus pocus....
We had that same problem on our Dodge pickup. No problem on the interstate but we had a drill when in stop and go traffic. I'd pop the hood and wife would run out and put an alligator clip on the battery to start the fan. Worked flawlessly for years!