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The Goodman B1378700 16-Pin Wiring Harness is a genuine OEM control harness for GMNT120-5D gas furnaces. This pre-terminated harness carries low-voltage and control signals between the integrated furnace control board and connected components through a keyed 16-pin connector. Melted connectors, corroded pins, chafed insulation, or intermittent no-heat faults traced to bad wiring are all reasons to install a fresh factory harness rather than splicing individual leads.
The OEM Goodman harness arrives with the correct 16-pin connector, wire gauges, colors, and lengths for true plug-and-play replacement — no crimping or re-pinning. A generic harness or a build-your-own repair costs less but risks mismatched connectors and wiring errors on a safety-critical circuit; for control wiring, the direct-fit OEM part is strongly recommended.
Difficulty: Moderate to Difficult. Cut power at the breaker first. Photograph every connection, unplug the 16-pin connector and component leads, route the new harness along the original path, and reconnect. About 30–60 minutes; take care not to pinch wires against sharp sheet-metal edges.