my truck is a 91 v6 auto sr5 ex cab and lately hasnt been starting. ive replaced the starter and battery and every now and then it just goes click and nothing, sometimes its click and i can hear something clicking in the dash behind the glove box and sometimes its nothing at all. someone said it could be my satefy switch on the tranny cause its an auto, but i have no idea how to check or diagnose that issue. any help is much appreciated.

thanks