Why will your 1990 Buick LeSabre not start unless you pull up on the gear shift?

The most likely reason your 1990 Buick LeSabre won't start unless you pull up on the gear shift is a faulty neutral safety switch (NSS). This switch is a crucial part of the car's safety system. It prevents the engine from starting unless the transmission is in Park (or Neutral, depending on the specific model and setup). If the switch is malfunctioning, it might not register the correct gear position, and thus won't allow the starter to engage. Pulling up on the shifter might be momentarily forcing the switch into a position where it registers neutral or park, thus allowing the car to start.

Other, less likely possibilities include:

* Worn shifter cable: A worn or damaged shifter cable might not be properly engaging the NSS.

* Wiring issues: There could be a problem in the wiring between the NSS, the ignition system, and the transmission. A corroded connection or broken wire could interrupt the circuit.

* Faulty ignition switch: While less common in this scenario, a failing ignition switch could also be contributing to the problem.

It's highly recommended to get this fixed as soon as possible. Driving a car with a malfunctioning NSS is unsafe. A qualified mechanic should diagnose and repair the issue to prevent potential accidents. Replacing the neutral safety switch is generally a straightforward repair for a mechanic.