[SiriusHardware]

I agree that it would be undesirable to have hard +5V on the keypad edge connector because the connector is not keyed, therefore +5V could end up anywhere in the event of a mishap.

A compromise might be, rather than take hard +5V to the edge connector, take it via a 470R or 1K resistor - a low enough value to take the reset input up to logic 1 against the action of the already existing 4K7 pulldown resistor. If a slip does occur, the resistor will limit the current and therefore the damage.

My Pi version of the uploader was made to use with my issue II MK14 which does not have reset available on the edge connector, but because it is a 40+ year old museum piece and possibly quite valuable I would not consider applying even the smallest of mods to it now.

For that one I just used a pair of flying leads with test clips attached to the leads of the reset capacitor as mentioned by Slothie. (See image). Not pretty, but it involves no modification to the target machine and since the connections are directly to the reset capacitor it does not care whether the machine is active-high reset or active-low reset as long as the opto collector goes to capacitor + and the opto emitter goes to capacitor - . The 120R resistor in series with the collector is to prevent the opto transistor from discharging a fully charged capacitor through itself without any current limiting.

I am not aware of a single legacy add-on or project which used either of the 0V connections on the keypad edge connector, although some individuals may have used one or both as a handy place to pick up 0V from on their individual system builds. The external keyboard itself does not require 0V. 0V would however come in handy if you used a non-isolated interface scheme which required a common 0V between the interface and the MK14.