System and drive reset switches can be added with front panel
switches to existing circuitry without removing the motherboard from the
chassis, as follows. I always liked to add a 100 ohm resistor in series
of any switch I installed just in case I made a mistake... the resistor
prevents any damage if I got it wrong.
     To enable a front panel system reset, you need to run two wires
from a momentary push-button switch to the 556 reset IC U27. One wire
goes to pin 8 of that IC and the other one to ground or pin 7. U27 is
located near the expansion/cart port.
     To enable a front panel drive-only reset, two wires from a
momentary push-button switch go to pin 5 of U16 and ground or pin 7. U16
is located near but to the left of the expansion/cart port.