Where is the idle air control switch on a 1988 5.0 liter f 150?

The 1988 Ford F-150 5.0L doesn't have an "idle air control *switch*". Instead, it uses an Idle Air Control (IAC) valve. There's no separate switch; the valve itself is controlled electronically.

The IAC valve is located on the throttle body. The throttle body is situated on top of the engine, where the intake manifold meets the air intake system. The IAC valve is a small, usually cylindrical component, often with one or more electrical connectors attached. It's directly integrated into or very close to the throttle body itself. You'll need to look closely at the throttle body to locate it.