Pin 3 on X26/7 goes to Pin 1 of the ARA 2-pin connector. It looks just like the ELR connector, but is only required for manual transmission cars. If your IP doesn't have the ARA solenoid, just leave that connector free.

A bit late for Corners, but hopefully useful to someone in future.

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1995 W202 C250 Diesel, OM605 NA engine, 5-speed manual
1986 W123 200, OM617 NA engine, 5-speed manual, rev counter
1989 W126 300SE, 5-speed manual