Wiring
Wiring is what many people consider the hardest part of any nitrous system installation. It is also what many people rush and therefore mess up. If you take the time to wire the system properly you will have a very safe and reliable system. The system should always use a relay and a wide-open throttle switch. On modular Ford engines, particularly those which use a plastic composite intake manifold, a special precaution must be taken to avoid fuel puddling and subsequent explosion. With direct port fuel injection the plastic intake manifolds were never designed to carry atomized fuel and air. As a result their ultra smooth internal surfaces do a poor job of keeping nitrous and fuel in suspension. At low rpms the air flow within the intake is relatively slow and can cause fuel to puddle in the intake. This can result in a backfire which easily demolishes the plastic manifold.

To prevent this problem the nitrous and fuel solenoids should only be activated when the engine is at wide open throttle and above 3000 rpm-an engine speed where the airflow into the intake is fast enough to keep the fuel atomized. This activation of the solenoids at this rpm is controlled by an electronic device known as a rpm window switch. The switch actually provides ground for the micro throttle position switch, which in turn activates the solenoids. The way the entire system works is three fold. First, a master "Arming" switch, usually mounted in the cockpit, must be turned on. Secondly, the engine must be at the "on" rpm as set in the window switch. Finally the throttle position must be at wide-open throttle thus activating the micro throttle switch. The rpm window switch simply provides a ground for the micro throttle switch, so if the rpm of the engine is not at the designated point the circuit is not complete and the micro switch cannot activate the solenoids. The RPM window switch also has an "off" rpm at which the circuit is broken.

The main components of the nitrous electrical system (clockwise from top left); wide open throttle micro switch, arming switch and relay, solenoids, tach adapter, and rpm window switch unit.	Use a relay harness to easily make the connections. See the side bar on relay wiring to understand where to make the connections.
We made a simple bracket and mounted the micro-throttle switch to the upper intake plenum. The switch is activated when the throttle is fully open and the cable arm swings up and hits hits switch lever. Wire the positive side of the switched, marked "NO for normally open" to the relay. The ground terminal connects to the purple wire of the BMN window switch.	The solenoid wiring has no polarity. Properly ground to chassis one wire from each solenoid, and connect the remaining two wires to terminal 87 on the relay.
Due to the coil on plug ignitions on these 4.6L engines an Autometer Tach Adapter is required to feed the rpm signal to the window switch. The Tach Adapter runs off this coil trigger wire (pin#34) located in the computers wiring harness on the passenger side fender in the engine compartment. Do not look for a pin #34 or similar trigger wire at the PCM.	Pull back the plastic wire loom to reveal a section of the red wire which connects to pin #34. Cut the wire and connect the solid red wire from the Tach Adapt to the side still attached to the connector pin 34. Connect the red/green striped wire to the other side of the harness red wire. The black wire of the Tach Adapt goes to ground, and white wire is the rpm feed to the window switch (it can also run an aftermarket tachometer or shift light.)
The RPM window switch is the heart of our nitrous activation system. This one is made by BMN Racetech and runs $130. It works by providing the ground to the microthrottle switch only when engine rpm's are in the selected range. Under the cover are dip switches and selector switches to set the number of cylinders and rpm on and off points. Three LED's (power, brake, and rpm) indicate when you have wired it up properly, as outlined in the next step.	We mounted the rpm switch in the glove box using velcro. Wiring it up is simple. The red wire is ignition-on 12V. Black is ground. White goes to the Tach Adapter feed from step 6 (also a white wire.) The purple wire connects to the ground terminal on the micro-throttle switch. Finally the brown lead splices into brake light switch above the brake pedal - this offers a quick way to kill the nitrous by tapping the brakes. The switch also has a first gear lockout option which can be activated to disarm nitrous in first gear to minimize traction loss.