I traced out that cable on the free 767 service manual from hifiengine.com. Pin 1 is on the left side.
1 - Right channel audio path output, prior to bass/treble. Goes through R334(4.7K) to line out right (J101-B).
2 - Left channel audio path output, prior to bass/treble. Goes through R333(5.6K) to line out left (J101-A).
3 - Ground
4 - Ground
5 - Power(~12V) - originates at fusible resistor R224(4.7), the other side of which ties to Q110, a ripple filter tied to 15V.
As soon as pin 5 enters the IO board, it goes through R323(560) which supplies ~10V to the line-in preamp(IC401 pin 4).
The only damage I could see happening from shorting pins on that connector together is pin 5. If you're sure you shorted together pins then they were probably adjacent to each other. So, I'm guessing you grounded the power supply pin (4+5).
R224 is probably fine, fusible resistors take time to blow. But such a small value means that it's possible it allowed Q110 to blow, essentially cutting power to a number of circuits.
Measure the voltage on pin 5, if it's not at least 11V, you may have a bad ripple filter. Measure the voltages on Q110, you should see 14V at the emitter, 15V at the collector, and 14.7V at the base.