Hi I have a 91 civic and I have replaced the main relay the dristrubitor and all its componits including the plug wires and plugs and I got another ecu out of the salvage yard and my ? Is why would the main relay buzz when the ignition is on or when trying to start the car any advise on the situation would be apriciated thanks.:confused:

It will buzz if the ECM is bad. The ECM controls main relay terminal 8, which is a computer controlled grounding terminal. Run the K-Test on your ECM, which is described in Section A below:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-honda-civics-46563.html