MB oil pressure sender

["Jouko Haapanen" <joukoh@vtoy.fi>]

My oil pressure light has started coming on intermittently around 3-4k rpm
today, and once warm at even lower rpm while loading engine.  I suspect the
sender, but as fate would have it, the sender for the MB also fits KW (Sport
q) and GV (Swizerland), guaranteeing stock in our parts dep't. NOT.  There
are two connectors on the sender, but one of them has no wire on it.  ETKA
tells me 0-5/1.8 bar for the sender, how can it relay this info with just
one wire? (stupid question of the day...)

Why just one wire???

I haven't yet measured the pressure since the sender is a PITA to get at...

FWIW, the engine is basically new rebuilt with 2000km since rebuild, oil
0W-30 Castrol SLX synthetic.