Lesson 8: What are the Different Starter Solenoid Terminals?

Learning objectives: 

at the end of the lesson you must be able to:

1. Describe the role of each terminal in the operation of the starter circuit.

2. Value the importance of correct terminal identification for ensuring safe and functional starting systems.

Many DIYers wonder: What wires go to the starter solenoid? Typically, a starter-mounted solenoid has three terminals with three connections:

The “B” or “battery” terminal: The terminal that connects the solenoid directly to the positive battery cable.

The “S” or “start” terminal: The terminal that receives power from the ignition switch.

The “M” or “motor” terminal: The terminal that attaches to the cable that connects to the starter motor.

When the driver turns the ignition key to the “start” position, voltage is sent to the starter’s “S” terminal. That voltage energizes the solenoid’s electromagnetic windings.

The windings then create a magnetic field that pulls the starter’s plunger, forcing it to push a disc against a set of contacts. Those contacts attach to the solenoid’s “B” and “M” terminals. Once the two terminals have an electrical connection, current can travel directly from the battery to the starter motor to crank the engine.

FAQs About Wiring a Starter

A licensed mechanic is your best source of information about wiring a starter. If you want to learn more but don’t have time to stop by your auto repair shop for a consultation, you might find the answers to these questions helpful.

Where Does the Starter Get Power?

The starter draws power from the battery through thick cables that can channel high electric current.

What Wire Goes Where on a Starter Solenoid?

Two cables usually connect the battery to the starter: a red wire and a black or greenish-yellow one.

The red wire connects the battery’s positive terminal to the solenoid, while the other cable connects the battery’s negative terminal to the motor.

SUMMARY oF THE TOPIC

Starter solenoids typically have three main terminals, each with a specific function in the starting system. The B terminal (also called the battery terminal) is the largest and connects directly to the positive terminal of the battery, supplying constant power. The S terminal (start terminal) receives the signal from the ignition switch when the key is turned to the “start” position; this activates the solenoid. Some solenoids also have an R terminal (relay or ignition terminal), which was used in older vehicles to provide power to the ignition coil during cranking. In many modern systems, the R terminal may not be used. Understanding the function of each terminal is essential for proper wiring and troubleshooting of the starter circuit.