I'd check all your grounds. The battery ground and the chassis ground from the transmission to the body. Also check all the connections on the starter. You probably have a dirty or loose connection. And when you are pulling so many amp with the glow plugs on and the starter trying to kick on, you can't get enough to run the starter and glow plugs. The glow plugs stay on 15-20 seconds after the light goes out. So that might explain why you can start up okay when you wait.

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