1. Listen for Clicks (Easiest):
* Have someone try to start the car while you listen near the starter motor (usually located on the engine block near the transmission bellhousing).
* A single click: This usually indicates a low battery, a bad connection, or a faulty starter solenoid (part of the starter). Try jumping the car – if it starts, the problem is likely the battery, cables, or solenoid.
* Multiple rapid clicks: This often points to a low battery voltage or a bad connection.
* No clicks at all: This suggests a problem with the starter motor itself, the wiring, or the ignition switch.
2. Check Battery Voltage (Easy):
* Use a voltmeter to check the battery voltage with the engine off. It should read around 12.6 volts. Anything significantly lower indicates a weak battery.
* Then, have someone crank the engine while you check the voltage. The voltage should remain above 10 volts. A significant drop suggests the battery or cables cannot supply enough power to the starter.
3. Check the Starter Solenoid (Intermediate):
* Locate the starter solenoid: This is usually a smaller cylindrical component attached to the starter motor. It will have large battery cables connected to it.
* Bypass the solenoid (CAUTION!): This is a risky procedure if you're not comfortable with car electrical systems. Use insulated tools and be extremely careful not to short anything. You'll need a large-gauge jumper wire. Carefully connect one end of the jumper cable to the positive (+) battery terminal and the other to the large positive (+) terminal on the starter solenoid. Have someone try to crank the engine. If the engine cranks, the solenoid is likely bad. Disconnect immediately after the test.
4. Check the Starter Motor itself (Advanced):
* This requires removing the starter motor from the vehicle. This is a more involved task requiring mechanical skills and tools. You'll need a wrench or socket to remove the starter bolts and potentially a starter puller depending on its accessibility.
* Once removed, you can test it with a battery and a jumper cable (again, be extremely careful). If it doesn't turn, it's likely faulty.
5. Check the Ignition Switch (Advanced):
A faulty ignition switch can prevent power from reaching the starter. Testing this usually requires a wiring diagram and multimeter to test for voltage at the switch.
Important Considerations:
* Safety First: Always disconnect the negative battery terminal before working on any electrical components.
* Professional Help: If you're not comfortable performing these tests or if you're unsure about any step, it's best to take your car to a qualified mechanic. Improperly working on your car's electrical system can lead to damage or injury.
* Wiring Diagram: A wiring diagram specific to your 1990 Buick Century will be helpful in diagnosing problems with the starter circuit. These are often available online or from a repair manual.
Remember that a weak or failing starter often shows other symptoms, such as slow cranking or a grinding noise when starting. If you're experiencing any of these symptoms along with failure to start, a bad starter is a strong possibility.
