Can the 4wd switch go bad in a 1999 silverado cause truck not to into 4wd?

Yes, a faulty 4WD switch in a 1999 Silverado can absolutely prevent the truck from engaging 4WD. The switch is a crucial part of the system, and if it's malfunctioning, it won't send the correct electrical signals to engage the transfer case. This is a relatively common failure point in older trucks. However, it's only *one* possible cause. Other potential problems include:

* Transfer case issues: Problems within the transfer case itself (like a broken linkage, worn components, or low fluid) are far more common causes of 4WD failure.

* Actuator motor problems: The motor that shifts the transfer case might be failing.

* Wiring problems: Damaged, corroded, or loose wiring in the 4WD system can interrupt the electrical signals.

* Fuse or relay failure: A blown fuse or a bad relay related to the 4WD system will prevent operation.

* Vacuum system issues (if applicable): Some older 4WD systems rely on a vacuum system for engagement; leaks or malfunctions can prevent 4WD from engaging.

Before replacing the switch, it's recommended to have a mechanic diagnose the problem. They can test the switch, check the wiring, inspect the transfer case, and rule out other possible causes. Replacing the switch without knowing the root cause could waste time and money if the problem lies elsewhere in the system.