At one time I was told that GPS is not allowed on cars in Cambodia. Is that law still in effect? Is it enforced?

Never heard of a GPS ban. Using phones, petting crocodiles, nursing children, facetiming your sweetheart, steering while someone else jammed in between you and the door who's doing the pedals, and driving the wrong way down one way streets is all permitted, so I don't see why they'd even notice a GPS.

Google maps doesn't do turn by turn routing here, which is a bitch.