Bizzare electrical gremlin in wife’s Rav4

My wife has a 1998 Rav4. I had to disconnect the battery this weekend to put it on the charger, wife drained it by leaving the lights on all day. The battery is only about 18 months old, so it took the charge just fine. I re-connected the battery, started the car to make sure everything was good to go.

later this afternoon, I overheard a strange noise coming from her car. The electric radiator fan was coming on about every 10 minutes, runs for 15 or so seconds, and shuts off.
Keys are not in the ignition, ignition switch is in the “Lock” position. Other than starting the engine to check that it would start, the engine hadn’t been run in 3 days, and the daytime temp was about 50*F, so it wasn’t coming on to correctly cool anything down.


So... seems I have a relay, fuse, or something that is stuck in the “closed” position to make the fan run. Any ideas on what to do? How to fix/replace whatever it might be that are DIY straight forward and simple?

 

I'd be looking for the coolant sensor location.

Pretty sure electric fans can run with the vehicle powered down if the temp requires it (like right after stopping/shutting off) and that sensor, or it's connection, could be the culprit.