My first guess is that the OD relay is "dropping out", perhaps due to circuit board solder joint problems. "Tapping" the switch button probably just "picks" the relay again (it plays no part in keeping the relay on). Many OD relays have been resoldered successfully — more info in the 700/900 FAQ.

Here's how the OD control circuit works:

1) Fuse 11 (200) 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)

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