I tried testing the glow plugs resistance, but it just shows infinite/open between the plug itself, and battery ground on every single plug...I guess this means every single plug is bad? I had a thought...is it possible that my engine grounds are bad, and that's why it's showing open? Where are the block ground cables on this engine?

Thanks guys!

__________________
Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles