Hi, I Have A 1978 Merc 300D 5 cylinder, we are having problems with the spark plugs, firstly i am after diagrams and information on the glow plugs wiring and just general diagrams, secondly, any help on the issue, we have 12 vlots running straight to the first cylinder, 8 volts to the second, then 4 volts to the other 3, the last 3 glow plugs have resistors on them but the first 2 don/t, this isn't right is it ?? help needed please and thank you

 

How can i fix that then please help appreciated.