Most drivers use a Spal temperature switch to control when the fan turns on. Switches come individually or as part of a kit. When you purchase a Spal temperature switch by itself that means you must also acquire the relay separately. Spal tests all of their wiring designs to ensure proper mating and grounding to alleviate the possibility of shorts or blown fuses. However, it is the overall functionality of the switches themselves why they are convenient. You can choose a Spal temperature switch that activates an aftermarket car fan at 185F or 195F, with either one shutting off once the temperature reaches 20 degrees below activation.
There is a process as to how the switches work. An automotive relay harness is wired to the fan, which activates it when the relay sensor is grounded. It is this relay wire that is mated to an open Spal fan switch that connects to the coolant. As soon as the temp of the fluid reaches the preset of the switch (185F or 195F), your aftermarket car fan will turn on. If there is a problem with a Spal fan switch, it is easy to tell. Should the fan turn on when the relay wire is grounded out but does not when wired to the switch, then it needs adjusting. This quick diagnosis during and after installation is what makes a Spal fan switch so easy to use.
A basic setup includes using a water-resistant relay and connector. Relays are configured for 10/40 amps with 3/8" NPT wiring, which helps them pull tighter. The relay harness set requires that you use a Spal fan switch for activation. The only time this is different is if your aftermarket car fan takes more than 10 amps. Spal's HO (High Output) series fans need one relay and harness apiece in order to work properly.
It is crucial that you choose a Spal switch kit along with your fan. Using other forms of wiring is not recommended for installation, as this can lead to poor grounding and fusing issues. The switches and wires Spal offers were designed specifically for motor vehicle applications, both in size and material. You can find what you need on the UltraRev site along with other car fan accessories.