Abstract: A reliable diagnostic system for running power-up diagnostics, displaying power-up diagnostic results, and retaining a power system status history. First, a method of testing a processor module in a computer system is provided. A processor including a serial port reads processor module diagnostic test instructions from a PROM in a serial line controller through the serial port by way of a serial bus in response to power-up reset instructions. Next, a reliable connection of a serial control bus to the modules is provided. Accordingly, backplane connectors are provided including wide signal conducting elements having multiple solder connection points to the modules and backplane. The serial control bus is electrically connected to each module through the multiple connection points of these signal conducting elements. Also, an apparatus and method for indicating module failures in a computer system is provided.