Diagnosing Starting Problems:
So your Jeep doesn't crank over, but why? You'll need a multi-meter for this, if you are unfamiliar with using a meter, read my multi-meter basics writeup.
|First is the starter solenoid clicking?
|If it does click, then its a connection problem, bad starter, or dead battery. Time to check the connections.
|If the starter does not click, then you need to check and make sure the ignition switch is sending power to the solenoid. On the back of the starter you have one big wire that goes to the battery, and one smaller wire, you need to check the small wire for power with the key in the start position (Obviously you'll need a helper for this). If you don't have power there, its time to trace the wire and find out if it is broken, or the ignition switch needs replaced. If the small wire does have power, but you don't get anything out of the starter, you need at least a starter solenoid, its normally recommended that just go ahead and replace the starter too.
|Next check the connections.
|Make sure both connections at the starter are clean. Also make sure the battery terminals are clean. Remember that the starter grounds through the mounting bolts, and the bellhousing, so make sure its tight and clean.
|Check the battery voltage.
|Sitting there, the battery should have at least 12.5 volts. Anything between 12.0-13.0 is acceptable though. Time to check the voltage while trying to crank the motor.
|If you don't have at least 12.0 volts, either your battery is dead, or bad. If you have a charger, try and charge the battery. If you don't have a charger most auto parts stores will check and charge batteries for free.
|Check battery voltage while cranking the motor.
|If the battery voltage does not drop below 12 volts and the starter just clicks, the starter is bad. If the starter does actually turn over, the battery voltage needs to be at least 10.5 volts while cranking the motor over. If the battery voltage is less than 10.5 volts either the battery is bad, or the starter is bad and drawing to much amperage. Take the battery to be tested, again most parts stores do this for free. If the battery tests good, you know the starter is bad. If the battery is bad, replace the battery. After replacing the battery, check the voltage again while cranking the motor, as a starter placing to much load on a battery can kill a battery. If you battery is now above 10.5 volts while cranking, you are good to go. If it is still below 10.5 volts, your starter is bad.