Al was right about the Sun 3/200 - it was the PROM - more specifically the complete absence of the PROM - that left the diag lights on all the time. That board's been shelved for a while. The 4300 is up though - it was the NVRAM (someone had put it in backwards at some point during the board's lifetime). Fortunately I had another 4300 board (suffering from the "all lights on" plague) that I grabbed the NVRAM from and it now works fine (but 200+MB of memory makes the diag boot excruciatingly slow).