shifter cable adjustment help..

I have a 67 falcon w/170ci and cruise-o-matic that will randomly switch gears on it's own.. it will go from park to reverse randomly and it's getting dangerous had it kick down into reverse while working on it today and had the engine rev'd up a bit thank got i had the ebrake on. any help would be great. and im sure it's the cable because it feels odd when shifting. Just cant figure out how to adjust it. thanks in advance, RJ

The Proper way to adjust the shifter is to remove the bezel face, then place it back in park.
CHOCK the wheels, jack and support the car with a suitable Jack stand.
Loosen linkage at tranny shift lever and manually shift it into neutral then back to park.
Set the linkage that position.
Go back in the car and WD-40 or CRC or PB-spray the cable that lifts the gear selector lock lever.
Lube it up all good and then you will be good to go.