The report also shows graphs taken from the QAR that indicate that the quote 'weight on wheels switch' unquote was working correctly, BUT, the switched ground from the nose wheel is in fact routed through 2 such switches on the nose wheel before being wired to the X2 terminal on the R2-5 relay. I am not familiar with the MD-80 series but my experience is that these switches on other aircraft are invariably in highly exposed areas and subject to all the muck and filth of dirty, sandy, wet runways whilst the relays themselves are in a far more benign environment and that hence the switches rather than the relays are more likely to fail, normally to some indeterminate state, neither one thing or the other
From the looks of the schmatic that PJ2 posted the two switches also operate 2-212 relay along with other relays. The "D" set of contacts reports to the flight recorder, I would suspect that the investigators would have picked up on that.
VFD