90 300zx 5 speed n/a, no power to ecu ( HELP PLEASE )

Okay my car a 90 z32 manual n/a and a mechanic checked it for me he said that when the key is in the on position, no check engine light is on and it should be on thought because every car is like that, and he said that the ecu is not being powered, there is no power in the ecu when the key is in the on position, he checked all fuses and relays, all good.... any idea guys????? Please help...i need this thing solved by 9/10 so I can take my woman on our one year, because thats what i took her in last year, so any help would be appreciated, and I dont have alot of mulas to go straight to the nissan dealership...help please!