[ray_mcavoy]

The optional factory gauge cluster in these trucks uses an electric temperature gauge. A single wire (typically dark green) runs from the instrument cluster, out through the firewall bulkhead connector, and through the engine wiring harness, to where it plugs into the temperature sending unit on the engine. The standard warning light cluster contains "hot" and "cold" lights instead of an actual temperature gauge. It uses 2 wires (typically light & dark green), one for each light. The wires follow a similar routing and plug into a 2-terminal temperature switch on the engine.

The Bosch gauge you purchased sounds like it is a mechanical temperature gauge. That design has a bulb that fits into the engine and is permanently attached to the gauge via a capillary tube. Removing it will ruin the gauge. Installing this type of gauge requires drilling a hole through the firewall that is large enough for the bulb (and attached nut) to pass through. And there should (hopefully) be a rubber grommet included with the gauge to seal up the hole and prevent the capillary tube from chafing on the edge. Also be sure to route the tube away from any other sharp edges, moving parts, hot exhaust, etc.