Our older 240's do not have the style of airbox and fittings you mention. I believe what you are describing is a later model arrangement to allow connection of an air tube for filtered air injection into the exhaust ports in some engine versions.

You could do what I did on my daughter's 940: file a tiny notch in the rim of the airbox where the filter's rubber edge fits and feed the thermometer sensor wire through there so the sensor just hangs in the space. The rubber edge seals off any unfiltered air leakage, and the notch prevents the wire insulation from being cut when you clamp the lid on.
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Bob: son's 81-GL, dtr's '94-940, my 83-DL, 89-745(V8) and 98-S90. Also 77-MGB and some old motorcycles.