does not want to fire

Hi forlks, i'm finding a problem with my 2.0 ltr diesil 97 largo,the glow light light goes out after about 5sec's,if i count to 25sec's and try it will fire up,if i try before or after that then it won't.It's had new glow plugs and iv'e replaced the plug relay located at the side of the battery.Q: is the a timer relay any where that i may replace to stop my light going out be fore the plugs are ready.
Dragonfish.javascript:emoticonp('')