The brake light switch screws into the pedal box and has a small retainer nut. You have to make sure the install depth is right so that the lights come on at the right time (just look at how the old switch was and do the same). It isn't that easy of a job because they didn't leave much room to get it in and out. Very doable DIY, but it is a tight working area.
It would be the reason for the shift problem.
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I do not check PMs. Call or email if you need something.
ECR is not a parts source. We are not in the mail order business.