To find the location:
1. Identify your axle: Look for markings on the axle housing itself. This might require getting underneath the truck. The axle type is usually cast or stamped somewhere on the housing. A VIN number lookup (with a vehicle identification number decoder) can help determine the original axle type.
2. Once you know the axle type: Search online for "2004 Dodge 1500 [Axle Type] rear axle drain and fill plug location." Many forums and websites have photos and descriptions. You can also search on YouTube for videos showing the process.
3. Visual Inspection (with caution): Get under your truck (safely supported on jack stands) and look carefully at the differential housing. The fill plug is usually higher than the drain plug. The drain plug is typically a lower bolt on the differential. They're often square or hex-shaped.
Important Safety Note: Always use jack stands when working under your vehicle. Never rely solely on a jack. Wear safety glasses. The differential fluid will be hot if the truck has recently been driven. Allow it to cool down before draining.