I know for me, my biggest concern was frying Megasquirt when I first powered it on,
so before I plugged Megasquirt into the harness, I turn the ignition on, and used a multimeter on the DB37 plug, to make sure 12volts and earth were on the correct pings
after I was happy with that, I turned it all off, and connected megasquirt into the harness,
I made sure it was quite, then turn the key to 'on', listening to make sure the pump started, and no other noise was heard,
then turned the key to start, and waited for it to fire..
I did preconfigured megasquirt when I had it plugged into the Stim, so I knew it 'should' fire with the setting I had used.
once it fired, I was very relieved..
then the fun part, tuning..
Nigel