I confess I am baffled!!
I deleted the existing 67_Pembrey file and re-downloaded from the original source.
Ran the installer, watched all the files get extracted and loaded, 100% complete, "finish". Check with windows explorer and the folder exists in "PnG/Game Data/Locations " labelled 67_Pembrey. Open folder and there are a list of files as I would expect.
Close explorer and start PnG.
Select car, ...........OK.
Select circuit..............anything you like but there is no Pembrey??!!
OK, try lobby and server get onto Lobby and server list................."track not installed" message??!!
But there is definitely a track folder in the right place when I examine the PnG directory.
Repeated the process with Geoffers link, with exactly the same results??!!
I assume that there is not a maximum number of tracks allowed in the "Locations" file. I know this can be a problem in GPL, not sure if it applies in PnG?