1976 Tradewind New fuse panel problem
The power on light is just that. As long as you have battery power, shore power or charge line power the light will be on.
Where is the opposite side of the power light connected? You say when you ground the grey wire, the light comes on.
Connect the blue charge line wire to a 30 amp fuse that will power the positive buss when connected.
Knowledge: "A gift to be shared. A treasure to receive."