The od is electric valve controlled. There's a wiring harness from the engine compartment down the trans tunnel underside to the od solenoid valve on the top of the tranny. There's a connector to check near the tunnel/firewall area.

Second, od enable is controlled by a temp sensor on the engine, behind/below the distributor cap. There are several sensors there. The one you want will have a single wire connection, and be one of the smallest. If the sensor is bad, grounding the sensor wire should enable od. You should see 12v at the sensor wire with ign on and od switch on.

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