vauxhall isuzu 4pin alternator problem

[Deo]

I have a problem with my alternator is not charging and bulb remains on. there is no voltage coming from the red/yellow wire but if I put a wire from + battery to the red/yellow wire it clicks the relay and start charging a healty 14v.

I tested the the relay it works ok. Also this is strange when engine is first cold start the relay works but as soon as I switch off the engine and restart the battery/charge bulb will not switch off !! ???

[Deo]

any help for me? still same problem the light on the dash just goes on after the glow plugs switch off around 8 minutes thats the engine is running.