That might be the problem. If the wiring is old and creating resistance the volt draw will be too much and the fans won't spin as quickly so they won't be cooling properly.

This has a massive impact on the speed which the fans will operate. My fans kick on and off quickly but I remember disconnecting the alt belt to work on the car and running it up to temp and thinking the fans had been on ages without switching off and the battery had only lost half a volt running the fans but they just weren't cooling enough. Belt back on and started it up and the fans sounded like they were running at twice the speed immediately.