Thanks for replys as for right now with temps. in the 30-40's the car has no trouble starting. I think all the g.ps. are working but have not checked them yet. I think when this happened about 2 weeks ago the light in the dash would work and then not work and eventually not go on all at which time I did find a bad glow plug replaced it and now 2 weeks later same problem. I am useing bosch g.ps. from A.Z. I read from a post today the light on dash is controled by a temp. sensor which on an 85 300 SD is located in the relay is this correct? Because if so maybe this is my problem if my glow plugs check out ok but yet the light on the dash is not coming on.