The GPS connector for the Nikon GP-1 GPS may not work or may intermittently work.
The rectangular hole cutout in the body of the Nikon is larger than the connector. It allows the connector to expand and cause poor electrical contact with extended use. The symptom is that your GPS unit will not work intermittently or at all.

I fixed the problem myself and saved $200 in repair costs or more. (and I did not need to send my camera away for weeks of repair time). Note that this may or may not work for you and it might just be a temporary fix.

Here is how to do it...

Just cut a small strip from a credit card (a credit card is the perfect thickness that you will need). Then shove that credit card strip between the metal connector of the GPS socket and the body of the camera. That forces the connector to compress and make a tight fit.

NOTE: If you cannot insert the credit card strip, use a small jewelers scewdriver to pry the metal connector away from the camera body, thus creating enough space for the card. Be gentle to avoid damage.

This is a photo of the Nikon D90 body with the credit card strip inserted.

Cut a small strip from a credit card about 3/4" long and 1/8" wide.
Then insert the strip between the GPS connector and opening in the Nikon body.
Bend the credit card strip to the left and paint with a black sharpie pen.
(NOTE: you could trim the card down to the surface of the camera body but then you may never be able to get it back out if you needed to for some reason.)