AC, Heater

AC & Heater Wiring – Climate Control Circuits

1939-1972 Passenger Car, 1939-1970 Merc, 1939-1979 PU

Within the Electrical system, the AC & Heater category covers the dedicated wiring that supplies, controls, and protects the vehicle’s climate circuits. These assemblies route keyed power from the fuse panel and ignition switch to the heater switch, blower resistor, blower motor, and thermostat switch where equipped. On air conditioned vehicles, the Air Conditioner Harness and Air Conditioner Wire extend that circuit architecture to compressor and control functions.

This category applies to 1939-1972 Passenger Car, 1939-1970 Merc, 1939-1979 PU exactly as stated. Heater Switch To Fuse Panel Wire establishes the protected feed. Heater Switch To Ignition Switch Wire ensures operation only with keyed power. Heater Switch To Blower Resistor Wire and Heater Switch To Heater Motor Wire complete the current path to the motor. The Heater Jumper Harness and full Heater Wire Set organize these leads into a defined routing layout under dash and through the firewall. AC & Heater Grommets, Heater Blower Motor Wire Grommet, and Heater Motor Wire Grommet isolate conductors from sheet metal edges. Air Conditioner & Heater Control Light Wire and Heater Switch Light Wire integrate illumination into the dash circuit. Temperature & Thermostat Switch Harness assemblies regulate cycling in applicable systems.

Electrical failures here are usually routing or resistance related, not component failure.

Technical & Fitment Notes

Climate control wiring must maintain uninterrupted current flow and controlled resistance. Loose terminals at the switch or resistor create heat and voltage drop, reducing blower speed. Corrosion at the fuse panel feed can produce intermittent operation that mimics a failing motor. Heater Blower Motor Wire carries full motor load and must remain properly supported and insulated.

Firewall pass-through points are common failure locations. Missing or hardened grommets allow conductor contact with sharp edges, leading to shorts and repeated fuse loss. Under-dash routing must remain clear of moving linkages and pedal assemblies to prevent abrasion.

Fitment will vary by model year or suspension configuration.

Examine wire condition, terminal tightness, proper ground and firewall protection before replacing switches or motors.