As noted in the previous post, the clip is installed first. Before attaching the moulding, make certain the clips are properly oriented up and down. I also inspected all clips to be certain the center pin was inserted flush and not protruding so as to interfere with the moulding. I'm inferring you are doing the lower moulding that runs underneath the doors and between the wheel wells. Make certain the moulding is clean on the underside metal. There are thirteen clip positions per side. Note that the entire length of the moulding is not perfectly straight. The forward portion takes a slight bend outward. This may be the more the challenging part of the moulding to attach. At any rate, position the moulding so its length matches the proper location on the car. Because of the length, you may want to plan on starting in the middle. The last one I did, I started at the rear and moved forward just to ensure I had the right starting point. Here is the magic. With your hands, press the moulding against the clip and the moulding will snap onto the clip. I skipped several clips and snapped on the moulding there. This helped support the weight of the moulding as I pressed on the remaining eleven. I kept a rubber mallet standing by. I was careful to match the moulding to the clip position as best as possible. The moulding could be attached in under a minute.

Mike
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'83 245 GLT, '90 760 GLT