I’m replacing my 69 factory idiot lights with a factory 69 gauge cluster. In the gauge assembly in the back near the bottom is a black tube. The tube is about 8 inches long and about a 1/8 inch in diameter. The tube enters the back of the cluster at an angle and looks to point right at the oil pressure gauge. In my idiot light assembly the hole were this tube would go has been covered with black tape. I don’t see the tube in the factory manual. The oil pressure gauge has an electric plug so I’m assuming the gauge is not mechanical. What is the tube for?