Electro Harmonix Crying Tone Wah. This pedal has been owned by me since the 15th September 1980. It was bought from Jones & Crossland Birmingham, and comes with the original box + receipt. 

    The wah has four tones - the deepest being suitable for bass guitar, a sweep reverse, and volume pedal effect.   The pedal is quite large for a wah / volume, and I believe this helps when using the pedal to be  smoother, and more accurate than other smaller units. There are some areas of wear on the case of the unit, but it is in good working order

Interestingly the reverse / inside of the box features a "Muff Fuzz Wah". 

I'm guessing the empty spaces on the circuit board could be used to make the conversion