If your vehicle isn't starting, it may be because of a damaged starter solenoid, the switch that fires a large current to the engine of a car or truck. A defective solenoid often makes a clicking sound when you turn the key, which means there's not enough power.

This lack of power is often caused from leaving headlights on, which drained the battery, or corrosion on the battery. Follow this guide to replace the solenoid:

Prepare to Replace the Solenoid

To complete this task, you need:

• work gloves
• colored masking tape
• floor jacks
• jack stands
• wrench set
• socket set  
• lubricant (optional)

Move the vehicle to a sturdy area, such as a concrete surface, with plenty of light, and turn off the engine. Let the motor cool for about an hour. Prop the hood, and look for the solenoid (a small cylinder or tube) on top of the motor or inside the engine compartment at the end of the red battery cable.

You may need to jack the vehicle front to access the solenoid. If you jack the vehicle, place jack stands on the back tires to keep it from moving. Check your owner's manual for designated jack stand points.

Remove the Old Solenoid

Disconnect the negative (black) battery wire by loosening the nut with the correct socket or wrench, and push the wire to the side. Stick a piece of colored masking tape on the three or four wires to mark their location, or take a photo. Detach each wire from the solenoid, and depress the clips on the wired pigtail to release it. 

On some models, you have to remove the starter before you detach the solenoid. In this case, use a wrench to remove the starter bolts and the starter, then set the parts aside. If you have trouble removing the hardware, spray it with lubricant.

Disconnect the bolts or screws holding the solenoid, and move it away from the starter as you grasp the starter with your hand. If you had to remove the starter, keep one hand on the solenoid as you detach the hardware.  

Install the New Solenoid

Take the old solenoid with you when you buy the replacement, so you will get the right fit. The new replacement should have the same number of wires as the old solenoid. If you can't find a solenoid with three wires, a four-wire solenoid will still work.

Insert the new solenoid, reconnect the bolts, then tighten them.  Don't reuse damaged bolts or screws. Reattach the starter, if applicable, and connect the solenoid wires. If the solenoid has four wires and you have three terminals, attach the third wire to the terminal marked "S." and don't use the remaining wire.

Contact a local truck repair service for more information and assistance.