replaced heater core and reinstalled the dash now i cant start engine or use anything electrical. i can hear a buzz from a relay and dome light comes on very dim while buzzing intermitently. checked all connections in dash nothing loose or unplugged. relay is located on top of a ''power block'' behind dash on driver side, removed 1 relay and it no longer makes a buzz. tried to switch with another but same result. OMRON 12088567 $20 ea. could this be the problem?someone said bad ground but where is the wiring harness grounded. checked all grounds underhood.

Did you disconnect the battery negative before you started. If you didn't I would check for a blown fuse.

If fuses are good check the grounds on left and right side of dash.
Let us know how it goes.