Thats true, but...
It depends upon the year and model.
68 B model (Pontiac, P8) cars do have a slightly different electrical system with a single wire to the pos. coil but so does the 65 Tempest/GTO and probably a few other years.

65 Tempest


Always make sure you're using the correct schematic. I have also noticed mistakes on the colored vinyl schematics that are popular with some. The 67 GTO/Tempest version is missing some important splices for battery power

 

I appreciate that, but it's difficult to decipher. I just purchased a '68 GTO with no ignition switch and lots of wires hanging under the dash. There's no rhyme or reason to any of them confusing. Can anyone please tell me which 2 wires turn the key on and then which one starts it? Where do they come from exactly so I can trace them? Thank you in advance.

 

The engine start and run circuits involve more than just the ignition switch. There's the neutral start switch, coil feed (2 wires for 68), 12 volts from the battery etc. I have a diagram but until they get the picture function working again, its going to be hard to explain if you're not an electrician or familiar with automotive wiring.
I should have something by tomorrow evening.

Are you missing the black plug which connects the wires to the switch?

 

Diagram of the 68 Ignition Switch.

RED - Battery (ALWAYS HOT)
BROWN & BROWN/WHITE - Accessory Circuits (Two Wires)
PURPLE - Starter solenoid through the NSS (Neutral Start Switch if Automatic)
PINK - IGN 1 (Coil Engine Running)
YELLOW - IGN 2 (Coil Engine Start)
PINK - Key Alarm (Small Pink Wire)
BLACK - Key Alarm
DK GREEN - Bulb Check for Water Temp Indicator Light