It is my understanding that for 67/68 the only factory installation of the emergency brake warning light was part of the convenience control package. The package includes four warning lights - (1) seat belt (based on timer), (2) emergency brake (based on a switch), (3) low fuel level (based on a unique fuel level sending unit and interposing relay), (4) door ajar (based on two switches, one per door latch).
All four lights were round with chrome bezel. The default location was the center dash panel. If A/C was also optioned, since the center vent supplanted the four indicator lights. the lights were located in the lower console. That means that if someone ordered the convenience control package, and A/C, the lower console would be a requirement. That would cascade also to require a radio. But I digress.
The under dash implementation of the emergency brake is IMO yet another Ford aftermarket/over the counter/dealer installed option, not factory.
The first 3 pictures below are from A/C vehicles. The last picture from a car without A/C