The trap pedal, much like the trap itself and the proton pack went through several subtle changes between the films.
The most obvious difference with the pedal seen in Ghostbusters is the inclusion of the 20 pin grey header as seen on the larger relay box. Certain GB1 trap pedals had black Dsub connectors. On this particular replica, it is grey. It’s situated on the smaller project box, near the connector that attaches the loom to the trap.
Here is a Ghostbusters 2 replica pedal. You can see the lack of the 20 pin header, the ribbon cable is instead held in place with a 20 pin card edge connector. As stated, the differences are very minor with the pedal.
Construction of a pedal is relatively simple, probably one of the easier props to build. From the the base plate, two project boxes are screwed in place, with numerous holes to fit the various components. A hinge is added to the rear attaching to the pedal vector plate. For the bellows under the pedal, there are many alternatives to what to use. Some use air conditioning tubing, others have used rubber suspension covers, similar to that seen on motorcycles. Many of the trap pedal parts can be bought here http://www.gbfans.com/shop/trap-parts/