Hi Howell

This is how I get the engines started after loading the 727-100 Cold-n-Dark (KSEA) provided by Captain Sim.

At the Engineers station.
Master Battery Switch..........................................ON
Essential Power Selector.......................................APU
AC Meters Selector...............................................APU
Left and Right A/C Packs.......................................OFF
APU Master Switch................................................Start
Once APU is started
APU Generator Breaker Switch...............................Close

At the Pedistal
Engines 1, 2 & 3 Mixture.........................................START (Ctrl+Shift+F4)

On the OH Panel
Engine 1 Starter Switch..........................................GROUND
Wait until it is running then...
Engine 2 Starter Switch..........................................GROUND
Wait until it is running then...
Engine 3 Starter Switch..........................................GROUND
Wait until it is running then...

At the Engineers Station
Left and Right A/C Packs.......................................ON

It's then up to you to configure the rest of it.  ;)
Hope this helps.

Mark

Edit: For some reason the power fails after some time. To get it back just press Ctrl+E (default for engine start) and within a few seconds you get the power back. I entered the following line in the aircraft.cfg directly under the [Electrical] electric_always_available=1 and then the power stopped failing.