Relay basics

Most car enthusiasts have heard the word “relay” at some point in their electrical escapades. Odds are your modern daily driver is loaded with them, and your project car probably has a few diligently switching away as well.

So you know the term, and have seen (and possibly heard) the small sealed boxes in place in various locations throughout the car, but you might not know how they work or why they are necessary.

One of the most basic functions is to use low-current switch to control a high-current circuit. Relays also help eliminate voltage drop, because you are no longer required to wire amp-hungry items directly from the switch to the load. As a bonus, this can help prolong the life of a switch, and allow for more high output gadgets with minimal impact on the electrical system.

Every standard relay 40 amp relay will require the following connections. The colors listed would follow in line with the GM color-coding used in each of our relay kits:

  • Battery/ignition source: This is the (red) 30 circuit.

  • Ground: This is the (black) 85 circuit.

  • Trigger: The (pink) 86 circuit.

  • Output: This is the (orange) 87 circuit, and will be what supplies power to the component when the relay is active. 87a is the relay at rest. The switching action between these two positions is what generates the telltale click we all know so well.

AAW offers a number of different relays; some of which are non-standard, or have been designed for a specific purpose. No matter how they are used, each relay kit will use circuits from the list above in order to function.