I live in the Southwest where temperatures well over 100 degrees are common in the summer. I want some way to manually turn on my engine cooling fan while sitting in traffic or in the staging lanes at the dragstrip. It is possible to tap into the lines that run between the PCM and the CCRM to force the fan on. But did not want to mess with those circuits. Instead, I added a relay, switch, and LED indicator to the stock fan circuitry, as shown below in red and blue.
When the relay and LED indicator are switched ON, the fan is forced ON. When the relay and LED indicator are switched OFF, control of the fan is returned to the car's computer.
16/18 gauge wire was used to connect the switch and LED and to make the connections to pins 85 and 86 on the relay. 10 gauge wire was used to connect relay pins 87 and 30 to the fan power lines.
The most commonly available relays are those that meet full International Standards Organization (ISO) specs. They can handle 30A current and under-hood temperatures of up to 135ºC I found one at Radio Shack for $5.99 (P/N 275-226). The rocker switch and 12V LED (with built-in resistor) also came from Radio Shack.
Before I could splice into the stock wiring harness, I had to locate the +12v 30A power lines that run from the battery to the CCRM and from the CCRM to the fan. Fortunately, they are easily accessible on the passenger side of the engine compartment. There is also a chassis ground nearby. On my 2000 Mustang, the battery-CCRM power line is yellow with a black stripe and the CCRM-Fan line is red with an orange stripe. The picture above shows the relay mounted on the radiator overflow bottle support, and my finished wiring after splicing. "X" marks the location of the splice points. The red wire loom that exits the top of this photo contains the single 18 gauge wire that makes the long run from the relay to the center console inside the car.
Here are the switch and LED mounted in the center console. I spliced into lines attached to the traction control switch (behind the console) to power the switch and LED. A pinout for that switch is shown below. Using the Ignition/Run feed as my +12v power source insures that this fan switch will operate only when the key is in the ignition and turned to "Run".
Notes:
- Whenever working on your car's electrical system, be sure to disconnect the battery as a first step. If you don't, you may damage the car's computer.
- Thanks to Kuplex, a forum moderator at 3.8Mustang.com, for the basic circuit diagram that got me started on this mod.
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