Yes, a agree with randy500, except one very minor thing: on my truck pink has power with key on and during start. I think the trucks may vary slightly between '67 and '72. Mine is a 1969.
Always-on power from the battery goes to the ignition switch on the red wire, and also to the top section of the fuse panel to power the brake lights, CIG lighter, and hazard blinker.
With they key in the on position, power comes out of the ignition switch on the pink wire to power the ignition coil or the HEI distributor's ignition coil and also to power the IGN UNFUSED terminals on the fuse panel.
Also with the key in the on position, power comes out of the ignition switch on the brown wire to go to the fuse panel lower section for radio, wipers, and AC blower motor.
Is it the engine that loses power and shuts off when throttle is released, or other things turning off such as blower motor or radio? I suggest hook up a test light or volt meter at the coil or HEI distributor verify you're actually losing electricity, and that you don't have a problem with the idle on your carburetor. You can use alligator clip test wires and a volt meter or test light to connect to the various terminals on the fuse panel to see where exactly you are losing power.
Here are some diagrams and links:
from this thread:
http://67-72chevytrucks.com/vboard/s...98#post8004798
Ignition switch diagram:
which is a snippet from main electric diagram:
http://67-72chevytrucks.com/vboard/s...27#post9186727