Thanks for your prompt response. There are two inquiries which i sent for help. The first one dealt with the inability to get the glow plug lamp to light when the car is being started. I reviewed this with the mechanic who installed a new glow plug relay with the expectations of solving the problem. The car is still hard to start and the light does not come on even though the mechanic applied voltage to the wire connected to the light and it lit as it was supposed to do - the light is good. I am looking at the scenario where it appears as if the resistivity of the glow plugs has increased significantly due to extended use and time. The mechanic measured the voltage on each glow plug during starting and all plugs had voltage on them - he still recommended that I install new glow plugs.
I checked the resistance of the plugs today in lieu of measuring the glow plug current on Monday to ascertain that the glow plugs are indeed bad - i think maybe two of them are bad after measuring the resistance. Four resistances were about one ohm each, while the other two were all over the place. Even though there was voltage on all the glow plugs, somehow the glow plug relay is sdtill not providing voltage to the glow plug lamp and starting is very difficult - maybe a broken Wire?.
Is there a thermal relay as well as the glow plug relay? If so, where would it be? I intend to go to the Mercedes dealer on Monday to look at electrical diagrams in order to solve this problem. Your advise please.