Hi. I have just fitted two to my Ute , I made a template out of stiff cardboard fitted it to the lights ( made a few before I got it right) then held it central over the existing parker and marked it out. Finally cutting out with curved tin snips.
Mark and drill mounting holes first so you do not overcut. the hole is approx. 50mm high by 30mm wide.
The light fitting has a thick rubber gasket that fits under it.
I had parkers in the head lights so I have made them daytime running lights like modern cars.
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