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The B1225020 is a genuine OEM wiring harness for Goodman GMT090-4A gas furnaces. This pre-terminated wire loom carries power and control signals between the furnace control board, gas valve, igniter, blower, and safety switches. Insulation that has cracked, melted, or been chewed, or connectors that have corroded, cause intermittent operation, fault codes, or no-heat calls — a fresh harness restores clean, reliable connections.
For a harness we recommend the OEM B1225020 — the connector pinout, wire colors, gauge, and lead lengths are matched exactly to the GMT090-4A, making it a true plug-and-play swap. Generic replacements almost never match a molded harness; mismatched connectors force splicing, which introduces failure points on a safety-critical circuit.
Plan for 30–45 minutes. Shut off power and gas, then photograph every connection before unplugging anything. Transfer connectors one at a time from old harness to new so nothing is crossed. Route wires away from hot surfaces and moving blower parts, and verify each plug is fully seated before restoring power.