Part Two: Wire It Up
ToMonitor the system, we're using electric fuel and nitrous pressure gauges and an air/fuel gauge from Dynotune to ensure we don't run lean while on the gas. Auto Meter also offers a trick three-gauge dashpod to cleanly mount the three gauges in the otherwise-useless dash cubby. | 
We can pick up fused 12V power and ground for all three gauges by T-tapping into the two wires leading to the cigarette lighter. | 
Rather than mounting a plethora of switches in the cab, we picked up this Nitrous Switch Center from Dynotune. The 2-1/16-inch NSC fits cleanly into a factory SRT-10 A-pillar molding we picked up from the Dodge dealer. |
We sourced power for the NSC, fuel pump, NMU, and purge solenoid from the post located on the fuse box in the engine compartment and spliced in 25-amp fuses on each. | 
The NMU is triggered by a wide-open-throttle (WOT) switch. Since Hemi engines don't have a conventional throttle position sensor (TPS) setup, we picked up voltage from the pedal position sensor (PPS). T-tap the wiring into the #5 pin on the harness located under the battery tray. To keep from running large amounts of voltage through the NSC, we installed 40-amp relays for both the Zex NMU and the purge, and mounted these on the airbox. Route the remainder of the wires from the NSC and the fused 12V power source for the heater under the wiper cowl and back to the bed alongside the fuel and nitrous lines. Install per Dynotune's clear instructions. Be sure to loom the wires for protection and zip-tie in place under the truck. | 
To control the fuel pump, we used the toggle switch supplied in the Zex kit (not used because of the NSC) and mounted it on the lower left side of the dash for easy reach. Aeromotive recommends at least 10-gauge wire be used for both the power and the ground for the pump. Run the 12V fused power from the fuse block post to the switch and from the switch back to pump in a loom for protection. Run a ground wire from the pump to the frame, but be sure to strip the frame down to bare metal and use a star washer for a solid ground. |
With everything wired, it's time to fill the cell and hook up the bottle to test for leaks. To avoid detonation when spraying nitrous, we're using VP Racing C12, a 108-octane unleaded fuel designed for a wide variety of applications. | 
After verifying there are no leaks, the final step is to set the pressure on the regulator. The regulator does require a vacuum source. Luckily, there happens to be a spare port located on the brake booster. Zex tests its fuel injection systems at 58 psi, so we set fuel pressure at 60 psi. Adjusting the regulator is easy; just loosen the lock nut and turn clockwise for more pressure or counterclockwise for less. | 
The final step in finishing the nitrous system is mounting the Zex nozzle. Zex recommends placing the nozzle 6 to 18 inches away from the throttle blade to allow for proper atomization of the nitrous. Using an 11/32-inch bit, mark your location and drill the intake tube. Using the supplied tap, thread the hole for the nozzle and install the proper jets for the selected horsepower (75, 100, or 125). |
As a precautionary measure, Zex recommends running colder heat range spark plugs to further resist detonation. On this Hemi, we installed NGK's 4306 plugs, which are one heat range colder than the stock 5306 plugs. As well, we ran a slightly tighter gap: 0.040 inch as opposed to the factory-recommended 0.044 inch. To ensure we have sufficient spark, we also installed a set of Taylor 8.2mm plug wires; misfires or weak coils could result in big problems, so we didn't want to take any chances. |  | 
Before remounting the Shaker hood, we fabricated the purge lines using bulk 3/16 brake line from the local auto parts store and a handful of compression fittings. The sky is the limit on the purge setup. Just be sure to route the lines so that the nitrous cloud is visible from the driver seat. Here, we routed the lines through the Shaker base plate and out of the openings on each side of the scoop. |