To date I find the electric fans the most difficult to install modification. Although difficult to install, the benefit was noticed right away, engine power, a.k.a. acceleration. These fans only run when the coolant needs to be cooled (that sounds funny).
It required many hours of knuckle scraping work. The most difficult part of the installation was in securing the fans to the radiator. You have to put your hand between the radiator and the transmission cooler.
Here is a shot of the overall installed kit. I wanted to make the parts look as close to factory as possible.
The temperature probes were just pushed into the radiator and held secure with silicone. At first I had my doubts about this but the probes haven't moved in over three years.
These are the attachment parts from hell. They consist of copper bars, rubber holdfast and a rubber piece with a metal clip imbedded in it. You simply push the copper rods through the fan, holdfast, radiator and finally into the clip. The clip can be a bear to start, especially if you can't get a good hold on the clip.
After a year or so of not knowing when the fans came on, I decided that something needed to be done in case the fans failed. My solution was to hook up an LED light to each fan. Now I know when the fans come on.