neutral safty switch

The neutral safety switch itself is a 3 post switch screwed into the drivers side of the trans kinda like a sender. It may be the problem but...
A 74 model has or had a seatbelt interlock that would interupt signal. The start relay on the left inner fender has a yellow wire the gets 12 volts from the ignition switch and a brown wire that gets a ground through the neutral safety switch. One wire or the other is interupted by seatbelt interlock. Thats all I know about it. Hope it helps