ECU diagnostic?

someone told me that the ecu in my car can tell me what is wrong with it with a flashing light or something?, can i get some more info on this? and another quistion, i want to convert my auto 89 VN to a manual and i was wondering what is involved and what parts i need? thankyuo

With the ECU, you turn a pot and it puts it into diagnostic mode, you run thru a couple of tests and it flashes at you the codes.
eg: 2 red flashes and 1 green = trouble code 21
You look up in your VN manual and find out what code '21' is.
As far as the Manual tranny goes, shouldn't be a problem, the VN's ECU didn't talk to the Auto.

:)

yeah i found that out a while ago, but thanks anyway :)