Automotive Relay Wiring Diagram - Pins 30, 85, 86, 87 for Lights, Horn, Fuel Pump

This document is a generic automotive relay wiring diagram showing how to wire a standard 4-terminal relay to control high-current accessories such as headlights, horns, fuel pumps, or fans. Power from the ignition switch feeds through a dash switch to relay terminal 86 (the power lead from the switch). Terminal 85 is the ground for the relay coil, shown routed to ground. Terminal 30 is the power lead from the battery, protected by an inline fuse connected to the positive battery post or the starter solenoid battery terminal. Terminal 87 is the switched power lead from the relay, feeding the load (headlight, horn, fuel pump, fan, etc.), with the load's other side going to ground. The legend at the bottom defines each relay pin: 86 = Power Lead From Switch, 85 = Ground For Relay, 30 = Power Lead From Battery, 87 = Power Lead From Relay. A reader can learn the correct pin assignments for a Bosch-style relay, where to place the fuse (between the battery and terminal 30), and how to trigger the relay coil from a low-current ignition-switched circuit. The diagram is generic and contains no year, make, model, wire colors, or part numbers.