Neutral Safety Switch. On the AW4 automatic, the reverse lamp switch and neutral safety switch are combined into a single unit. It's fan-shaped, about 3" across, and lives on the pax side of the transmission (go down to the shift lever on the driver's side, and go straight across. You'll find it.)
On manuals, the NSS was relocated to the clutch pedal (you had to have the clutch out to engage the start motor) and the reverse lamp switch was a bung in the side of the case.
If you have the automatic, the NSS costs a mint - but can be cleaned for about $10 in supplies (assuming you don't have any around to start with.) Do a search here for <cleaning + NSS> or similar, and you should be able to find a writeup or two - and my additions to make it simpler and more reliable.
If you have the manual, expect to just change the thing - but a replacement should be in the $10-20 range.
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