I have only Impala in game on POLICE slot because i wanted to do testing on my actual moderately modified GTA IV if lights are still bugged.
Other cars from NYPD car pack if have upper lights are too bugged, same as Impala but unmarked cars from NYPD car pack worked as they should.
Btw, i removed NYPD car pack and load other car pack with ELS .ini and they didn't have problem.
I don't understand this issue.
But like I said, on pure GTA IV all NYPD cars work as they should.
So there must be some faulty mod that spoils it.