1. Faulty Speaker: The speaker itself may be damaged or defective. Check the speaker for any signs of physical damage, such as a torn cone or damaged voice coil. You can also try disconnecting the speaker and connecting it to a different audio source to see if it works properly.
2. Head Unit: The head unit (radio) may be the culprit. Check the balance and fader settings on the head unit to make sure that the left side speakers are not muted or turned down. You can also try connecting a different audio source to the head unit to see if the left side speakers work properly.
3. Amplifier: If your Jeep is equipped with an amplifier, it could be the cause of the problem. Check the amplifier for any signs of damage or overheating. You can also try bypassing the amplifier and connecting the speakers directly to the head unit to see if they work properly.
4. Wiring: While you mentioned that the wires are all good, it's still worth checking the wiring again, especially the connections at the speakers, head unit, and amplifier (if applicable). Make sure that all the connections are secure and free of corrosion. You can also try wiggling the wires to see if there is any intermittent connection.
5. Grounding: Check the grounding points in the vehicle, particularly the ground connection for the head unit and amplifier (if applicable). Make sure that the grounding points are clean and secure, as a poor ground connection can cause audio issues.
If you have checked all of these things and the left side speakers are still not working properly, it may be best to seek the help of a qualified car audio technician to further diagnose and fix the issue.