If you need a "hard" switch that cuts power instantly when the key turns, check under the dash.
According to multiple Silverado owner forums, the most reliable and easiest place for switched power is the passenger-side dashboard fuse box. 2004-silverado-switched-power-source
This circuit is often controlled by RAP (Retained Accessory Power), meaning it stays on for 10 minutes or until you open the door after turning off the key. 2. Under-Dash Relay Panel (Above Brake Pedal) If you need a "hard" switch that cuts
There is often an unused relay socket (upper left) that provides 12V key-on power. This can lead to parasitic battery drain and a dead battery
Unlike older trucks, the 2003-2006 Silverado/Sierra trucks (GMT800 platform) are heavily controlled by the CAN-bus system, meaning many fuses in the dashboard remain live (constant power) even after you turn off the truck. This can lead to parasitic battery drain and a dead battery!
Finding Switched Power in a 2004 Chevy Silverado (Easy & Safe Methods)
Use an "Add-a-Circuit" (fuse tap) for a clean install. Note that this is often a 3-pin fuse slot, so you may need a specialized mini add-a-fuse.