That tan wire with a black stripe you mentioned is likely part of the system that prevents the engine from starting if certain conditions aren't met (like a security system, or a sensor malfunction). Disconnecting this wire is generally NOT recommended. Doing so could prevent the engine from starting, damage the ECM, or lead to other issues. If this wire is disconnected or causing problems, there's an underlying electrical fault that needs professional diagnosis.
Instead of trying to adjust the timing, which is impossible without specialized equipment and could seriously damage your engine, focus on diagnosing any problems you are experiencing. If you're having starting, running, or performance issues, you should:
* Check for trouble codes: Use an OBD-I code reader (suitable for your year vehicle) to retrieve any diagnostic trouble codes (DTCs) stored in the ECM. These codes will provide clues about potential issues.
* Inspect the ignition system: Look for damaged or corroded wires, spark plug wires, distributor cap, rotor, and spark plugs.
* Check the fuel system: Ensure you have adequate fuel pressure and that the fuel injectors are working correctly.
* Inspect sensors: A variety of sensors (e.g., crankshaft position sensor, MAP sensor) feed data to the ECM that influence ignition timing. A faulty sensor can cause erratic operation or prevent starting.
If you're not experienced working on vehicles, it's best to take your Suburban to a qualified mechanic for diagnosis and repair. Attempting to troubleshoot an electronically controlled ignition system without the proper knowledge and tools can cause more problems than it solves.
