So is this a '69 GTX (I assume from username) ?

Only electrical things I can think of in that area:
Starter & solenoid
AT neutral safety switch wires
On left frame rail, brake warning lamp wire
How those would cause shut-off, I don't know.
This is where a factory service manual comes in handy to look at the circuits.

Fairly common spot for the valve cover gasket to leak, and that can generate smoke.

Cleaning the bulkhead contacts is always a good idea if it hasn't been done before; it's just good maintenance.