How have you checked the glow plug operation? Have you checked the resistance of each individual glow plug? My opinion is that individually checking each plug, and checking for voltage at each glow plug while the relay is on is a good place to start.

SteveM.

__________________
'93 190E/D 2.5 Turbodiesel 5-speed (daily driver)
'87 190D 2.5 Turbo rustbucket - parts car
'84 Dodge Rampage diesel - Land Speed Record Holder
'13 Ram 2500 Diesel
'05 Toyota 4Runner