I just put new spark plugs in my 1967 GTX Hemi car that has power disk brakes. I am having difficulty getting number 7 spark plug wire back on.

I have the plug wire with the flexible insulator on number 7 to try and avoid moving the booster, but it seems that the rubber on the insulator is being pushed sideways before it can go over the tip of the plug. When I think I have it aligned and push down on the insulator to connect it, it pushes right back up and never connects.

Does anyone have experience with this and any suggestions on how to do this other than moving the booster out of the way?