How to Wire an Ignition Switch

by Michelle Schaefer

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The ignition switch in a motor vehicle is the main electrical component used by the operator to start, run and turn off the vehicle. The main purpose of the switch is to allow the operator to safely engage the ignition system and activate the electric starter. Replacement of the ignition switch becomes necessary when you have trouble turning on the electrical system, or if the starter fails to stop turning after the motor has started.

Step 1

Locate and identify the pins on the back of the ignition switch, There should be four terminals marked "BATT" for Battery, "ST" for Start, "IGN" for Ignition, and "ACC" for Accessory. Some switches may use a different letter or number code, so check with the manufacturer of the switch to properly identify the terminals.

Step 2

Disconnect the cable from the negative battery terminal using an adjustable wrench. Identify the positive power lead to the ignition switch. The power lead is usually a thick red wire and stays energized at all times. Install the correct terminal end on the power lead wire and crimp it securely with a terminal multi-tool. Connect the power lead from the battery to the "BATT" terminal of the switch. Some ignition switches use a cross-tip screw to secure the wires, and some use spade clips on the wire ends. Determine which one is appropriate for your ignition switch.

Step 3

Connect the accessory lead wire to the "ACC" terminal of the ignition switch using the appropriate wire terminal. This wire energizes vehicle accessories such as the radio when the ignition switch is turned to the "ACC" position.

Step 4

Connect starter relay wire to the "ST" terminal of the ignition switch. The "ST" terminal only activates when the ignition switch is turned to the "START" position and is a spring-loaded momentary contact.

Step 5

Connect the ignition wire to the "IGN" terminal of the ignition switch. This is the main terminal that is used for vehicle ignition, wipers, accessories and other operating features. This is the normal "run" position of the switch.