Back-up lights on in forward gears??

Hey everyone I put a 'new' (running from someone else's car) 904 transmission in my '70 Duster and for some reason the back-up lights come on when the shifter is in both forward and reverse gears. I put a new neutral safety switch in, could that be the problem or is there something else that could be causing it to come on in forward gears? It comes on in Drive, 2, and 1...