Why use an external GPS when the phone has a gps?
Do you have all the switches set to the “allow” position?
BTW if you are developing something yourself this howto I posted might help?
There are issues with the GPS antenna and as far as I’m aware there is no solution yet for the problem.
So attaching an external GPS module is an interresting experiment. 
Post ls -l output?
Can you amend the permissions / ownership after the fact (from root obviously)?
Some solutions may be unsatisfactorily secure but let’s take this as proof-of-concept and worry about security later. 
Which user?