The fact that it only starts with the seatbelt hooked suggests a *coincidence*, not a direct causal link. There's something else electrically wrong. Here's a breakdown of troubleshooting steps:
1. Check the Obvious:
* Battery: Test the battery voltage. A weak battery can cause all sorts of starting issues.
* Battery Terminals: Clean and tighten the battery terminals. Corrosion can severely impede starting.
* Starter Motor: Listen carefully when you turn the key. Do you hear *any* clicking from the starter motor? If not, the problem likely lies with the starter motor circuit itself (low voltage, bad connection, bad solenoid, or a failing starter). If you hear clicking, the battery or connections are suspect.
* Alternator: While unlikely to *prevent* starting, a completely dead alternator will prevent the car from running once started. If the car runs *only* with the seatbelt fastened, check this too.
2. Investigate the Wiring:
* Reconnect the Seatbelt System: Reconnect the seatbelt wiring (carefully and correctly!). While it's unlikely to be the root cause, it's important to rule this out completely. The problem might have been a short in that wiring that's now affecting something else.
* Check for Other Wiring Issues: Look for any other loose, damaged, or corroded wires, particularly around the ignition switch, starter motor, and under the dashboard. A corroded ground wire is a common culprit in older cars.
3. Advanced Troubleshooting:
* Ignition Switch: A failing ignition switch can cause intermittent starting problems.
* Immobilizer System (if equipped): Some 1992 Jettas might have had an early immobilizer system. If the system is malfunctioning, it could prevent starting. (Less likely, but possible).
* Fuse Box: Check all fuses, especially those related to the ignition system and starter motor.
* Relay: Look for any blown relays related to the starting system (check your car's manual or online resources for relay locations).
Important Note: The coincidence of the seatbelt and starting could simply mean a wiring harness issue is causing a problem that manifests when the seatbelt is connected (or disconnected). A faulty ground, or a short circuit somewhere, may be aggravated by the additional load created by connecting the seatbelt system.
Recommendation:
It's highly advisable to have a qualified mechanic diagnose the problem. Attempting further electrical troubleshooting without experience could lead to more damage. The fact that the situation changes based on the seatbelt's connection strongly suggests a wiring issue somewhere that needs professional eyes.
