Watts Happening

Wiring Electrical Relays Into A Nitrous System

Scott Crouse Feb 1, 2002 0 Comment(s)

Step By Step

One relay should be used for each switch controlling a load circuit. This relay can be purchased from MAD Enterprises.

As your vehicle becomes faster, it might be wise to use a throttle- activated (arrow) microswitch.

There are usually two solenoids for every stage of nitrous used. One for fuel, and one for nitrous.

This is a simplified schematic of how a relay is wired into a load circuit.

Notice the fuel-safety switch in the diagram. This is a great safety feature that all nitrous cars should have. Without adequate fuel pressure, the nitrous relay will not activate the solenoid.

If you have ever installed a single-stage nitrous system then you know there is more to this system than two solenoids and a couple of fuel and nitrous lines. The solenoids are electrically activated, which requires some minor electrical knowledge. Often it is the electrical side of a nitrous system that can be confusing or improperly installed. If these connections are not made correctly, there’s the possibility of burnt switches and improperly functioning solenoids. Before installing any system, it is best to understand the demands and capabilities of each component to be sure they all work together.

Nitrous systems are made up of several key components. Typically, each stage of nitrous uses two solenoids (fuel and N20) to deliver the correct air/fuel ratio into the intake tract. The nitrous solenoid is connected to the nitrous bottle via a steel braided line. The fuel solenoid is plumbed to a fuel source. Once these parts have been installed, it’s up to the electrical side of the system to ensure that the solenoids open and close properly. Wiring multiple-stage nitrous systems and timing-retard devices can become quite confusing, so to simplify our wiring schematic, we’ll look at a single-stage system without any external devices.

High-flow solenoids can draw large amounts of current depending on the system. A high-current draw from the solenoids can pull >> excessive amounts of amperage through switches that may not be designed to carry such loads. For example, a 100-175hp Super PowerShot system from NOS draws 0.6 amp at the fuel solenoid and 8.6 amps from the nitrous solenoid. The nitrous solenoid draws more current because the valve inside the nitrous solenoid must work against extreme pressure.

A standard nitrous system applies approximately 900 psi to the nitrous solenoid while a carbureted engine’s fuel system is likely to produce 5-7 psi at the fuel solenoid. NOS’s higher horsepower Cheater nitrous system increases the amperage load to 1.6 amps for the fuel solenoid and 10 amps for the nitrous solenoid.

The more powerful systems draw additional amperage because the valves inside the solenoids are larger, which means more surface area for the pressure to resist against. This 8 to 10 amps of current through a low-amperage switch can easily overload the circuit. The best way to avoid burnt switches and electrical malfunctions is to use a relay.

Relays are used to connect a high-load circuit to a power source when using a low-amperage switch. Most relays have five flat-blade terminals protruding from them. Those five connections are labeled numerically to identify each position’s function. The No. 30 connection connects directly to a power source (battery). The No. 86 connection is paired to the on/off switch (arming switch). The No. 87 connection is wired to the load (solenoid). The No. 85 connection is used to trigger the entire circuit (button or micro-switch). The last tab in the middle—No. 87a—is rarely used.

A properly installed, single-stage nitrous system should be wired from the battery through a fusible link to safeguard against unexpected power surges. Once the electrical current travels through the fusible link it can be routed to the relays. One relay should be used for each solenoid. Once the arming switch has been triggered, power is fed to each relay, and the circuit is hot. Upon activation of throttle-mounted microswitch (or in-cockpit button), the relay will supply electrical current to both solenoids to activate the system.

A good source for electrical knowledge and relay installation is MAD Enterprises’ Electrical Wiring and Universal Relay Kit handbooks. These handbooks illustrate the fundamentals of wiring and explain different relay configurations, electrical theory, and proper procedures for making wiring connections.


Mad Enterprises
Springville, CA
Dahlonega, GA 30533
NOS Nitrous Oxide Systems
Pomona, CA 91766


subscribe to the magazine

get digital get print