I doubt that the truck would be equipped with a yellow emergency button. This did not come out until the 70's. If his truck had a tractor protection valve, and a lot of 60's tractors didn't, it would probably be operated by a toggle type lever. It is the same toggle valve that is used today on sliding 5th wheels, power divider lock and suspension dumps. I think International's first year for the button was on their 4070B model which came out in 74. But it is hard to say what his truck has because it was common to retrofit as newer stuff came out. It is also very unlikely that a 66 model had spring brakes. If it did, it would probably be a chrome plated knob on a BW valve that you push to drive and pull to park.
