Joel, which specific decoders are you asking about?
The connections to the drop-in decoders are fairly simple. You have the track connections at the corners, then the motor connections. The headlights F0F and F0R pads are usually at the front and rear of the decoder board, and any additional function pads are usually documented in the decoder's installation manual.
The decoder is likely Digitrax DN166I1D (or maybe an older version of that decoder). If you go to the Digitrax website, you will be able to find all the documentation for that decoder.