Stewart, I use a spray on contact cement, such as 3M. I spray the new pad and the dash. I then make up 6 inch wide strips of a heavy gage poly vinyl. I lay the strips on the dash, side by side, lay the new pad on top. What ever you do, make sure it is in the proper position and then pull the strips out one at a time.
TIP! Make sure the pad fits the way it's supposed to before cementing, by shaving or sanding the foam backing! Once it's cemented, it's all over!
I also cut the gage and switch holes after the pads cemented in.