...Here is an overview of the control circuit:

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OD operation involves 4 components and the wiring that connects them...

1) Fuse 11 (200) or 12 (700/900) supplies voltage to items #2, #3, and #4.

2) The Shifter button/switch turns the OD relay off and on

3) The OD relay controls the Upshift ("OD off") Arrow light and the OD solenoid (separate wires). When the Arrow light is ON, the relay and solenoid are OFF

4) The OD solenoid allows OD engagement when ON, (the "default" OD relay/solenoid state at Key On)

If your shifter switch makes the Arrow light go on and off, then the OD relay is working. If not, start with fuse 12.

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NOTE: In your case, I'd also suspect a bad Arrow Bulb, because a "dead" OD relay should still provide a ground for the bulb, just as it does with a good relay that is "off".

--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.