I have an intelectron BC816P sound/light sensing timer, have had it a long time, someone messed with the settings and I don't know how to reset it. Is there a diagram/schematic of the faceplate that identifies each of the knobs/switches?

I have one of these too, and I just found the card it came in, with the instructions. It is a sound & light sensing timer.

The big rotary dial in the middle sets the time ON from 3-4 minutes (extreme counterclockwise) to 8 hours (full clockwise).

The adjustment under the light sensor on the right sets the sensitivity of that light sensor. Full counterclockwise represents nearly full darkness. Turn to the right to have the timer on when there's more light.

The holes at top left are the sound sensor, and the adjustment to their right sets the sound sensivitity. Full counterclockwise is the least sensitive position. The LED lights up when a sound is detected, so you can see what your sensitivity setting does.

The three-position switch on the bottom left selects the mode, from left to right: Sound Only, Sound/Light, Light Only.

In Sound Only mode, any sound above the threshold will turn on the power out for the duration determined by the big dial. Further sounds start that timer over.

In Light Only mode, the power will turn on when it becomes dark in the room, with needed darkness determined by the little dial on the right. It will stay on for the duration determined by the big dial. After that amount of time, it won't turn on again until after the room has become lighted again for a few minutes.

In Sound/Light mode, sound will turn on the power for the selected duration but only when it is dark in the room (as determined by the little dial on the right).