* Brake Light Switch Function: This switch is crucial. It does two things: it activates the brake lights when you press the pedal, and it also sends a signal to the vehicle's computer (or other electrical components depending on the specific year and model). This signal can be involved in things like safety features or even the idle control system.
* The Connection: When the brake pedal is pressed, the switch closes a circuit. If the switch is failing, it might be intermittently breaking the circuit, interrupting power to the engine's control systems and causing it to stall. The restarting afterward suggests the interruption is temporary.
* Other Possibilities (less likely, but worth considering):
* Vacuum Leak in the Brake Booster: While less likely to cause a direct stall, a severe leak in the brake booster could make braking unusually hard and might place an unusual load on the engine, possibly leading to a stall, especially if the engine is already running weakly.
* Alternator/Battery Issues: A weak alternator or failing battery might not provide enough power under increased load (like when braking and the brake lights are on). This is less likely because the engine restarts, suggesting the power issue isn't consistently severe.
* Wiring Issues: Damaged or corroded wiring related to the brake system or the engine control system could also cause intermittent problems, though this is harder to diagnose without specific symptoms.
Troubleshooting Steps:
1. Check the Brake Lights: The first step is to check if your brake lights are working correctly. If they're flickering, intermittent, or not working at all, the brake light switch is the most likely culprit.
2. Inspect the Brake Light Switch: This is usually located on the brake pedal assembly. It's a relatively small switch, and often easy to access. Visually inspect it for damage or corrosion.
3. Test the Brake Light Switch (if possible): Some brake light switches can be tested with a multimeter to check for continuity. Refer to a repair manual specific to your 1991 Chevy Astro van for instructions. This is usually the most definitive test.
4. Check the Vacuum System (if brake switch test is inconclusive): A mechanic can check for leaks in the brake booster system.
5. Consider Professional Diagnosis: If you're not comfortable with automotive electrical work, it's best to take the van to a mechanic for diagnosis and repair. They have the tools and experience to properly diagnose the problem.
The brake light switch is the most probable cause, but ruling out other possibilities requires a more thorough inspection. Always prioritize safety when working on your vehicle's braking system.
