START USING EXTERNAL POWER
1. Parking brake---CHECK ON (CTRL+”•”or directly by the handle)
SO UPPER PANEL--SELECT (FROM ICONS PANEL (SHIFT+2))
2. External power--CONNECT (SHIFT+G)
3. External power connected light (amber) --CHECK ON
4. Check Duct high (86) and low (87) pressure indicators rising
5. Ground service master switch (20)-ON
6. Power on BUS light (blue (19))-CHECK ON

Then....

START-UP USING ENGINE START SWITCHES GROUND START (Start engines 3, 4, 1, 2)
Make all BEFORE START ITEMS as described above (STEPS 1 trough 6), then:
1. LEFT & RIGHT WING VALVE SWITCHES (76-77) - OPEN (SO UPPER PANEL)
2. Engine start switches (40-43) of the respective engine — START & HOLD until EGT increases
(OVERHEAD (OH) PANEL)
After all engines are stabilized at idle:
1. Generator circuit breaker switches (34-37)—CLOSE (observe lights coming out)
2. Another after start items—AS DESCRIBED ABOVE

You can find all this in the manuals which can be downloaded from: http://www.captainsim.com/products/b707/manual.html

Cheers!  :)
Jim