Things You'll Need
The starter in your GMC Sierra is dependent on three pieces of equipment. First, the ignition switch sends electrical current from the battery to the starter solenoid. The solenoid then forces the gear in the starter housing to engage the engine. When the starter motor turns on and spins the gear, the engine roars to life. If any of these stop working, it means the starter won't turn over in your GMC Sierra.
Mix a 50/50 solution of baking soda and water and clean the battery terminals and battery wire connectors with the solution. Use a wire brush to apply the solution. This cleans old corrosion and battery acid off the battery terminals. Attempt to start the car; if it does not start, move to the next step.
Check the voltage output of the battery. Place the red lead of a multimeter onto the positive battery terminal. Place the black lead of the multimeter on the negative battery terminal. If the battery reads less than 12 volts, charge it or replace it. If the battery reads higher than 12 volts, the battery is not the issue. If the Sierra does not start after replacing or charging the battery, move to the next step.
Turn the headlights on and then turn the ignition key to the "On" position. If the headlights dim, the ignition switch sends electricity to the starter motor and solenoid. If the headlights do not dim, the ignition switch is defective.
Locate the starter. It bolts onto the driver's side of the transmission housing. The solenoid bolts to the side of the starter motor. Locate the two wire connectors on the back of the solenoid. The wire on the left connector connects to the ignition switch. The wire on the right connector connects to the starter motor.
Place the blade of a screwdriver across both contacts to short out the starter solenoid. This makes a direct connection between the starter motor and the ignition switch. Have a second person turn the ignition switch to the "On" position." Because the solenoid is shorted out and will not kick the starter gear into the engine, the Sierra will not start. However, the starter motor should turn on. If the starter motor does turn on and makes a humming sound, the starter solenoid is defective. If the starter motor fails to start or runs roughly, the starter motor is defective.