If you have the 4sp auto 42RLE then the only switch I can find relevant is the Transmission Range Switch.43RLE Bottom left picture switch number 3. Again called a TRS. The other two are input and output switches.
If however it is the 3 speed auto either the 30/32RH unit then it is a 3 pin neutral/safety switch. location
That might look something like this, 3 pin
Based on that location picture, I think we are looking at an upside down view of the tranny. As that looks a lot like the edge where the pan sits. So I'm going to say left hand side, lower.