I went rooting around my engine compartment to trace an unrelated issue and found crusty ground wires near the throttle cable area. Insulation cracked, wires exposed, etc.
My main harness was replaced years ago, but when I played with these wires, my oil pressure gauge needle jumped around like crazy!
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car