Get the electronics parts you need for your amp effects control foot pedal, which are a metal or rugged plastic project enclosure, a heavy-duty metal push-button SPST on-off switch and a 1/4-inch monaural phone jack for connecting a standard guitar patch cord to your amplifier's foot-pedal input jack. Get four self-adhesive rubber feet for your project enclosure if they're not included with it. These prevent your foot switch pedal from sliding around when you use it. You can find a variety of small project boxes and the other necessary parts at your local electronics store or an online electronics parts supplier.
Use your basic electronics tools to build your amp foot pedal. You'll need a soldering iron and electronic rosin core solder, needlenose pliers, wire cutter/stripper, Phillips-head screwdriver, small round file and a drill with a 3/8-inch drill bit. Also, cut two 6-inch lengths of single conductor hookup wire to use for connecting the push-button switch to the 1/4-inch phone jack.
Begin building your effects control foot switch by using the drill and 3/8-inch bit to drill a hole in the top and rear panels of your project enclosure for mounting the pushbutton switch and 1/4-inch phone jack. Use the round file to smooth the inner and outer edges of these holes. Use the needlenose pliers to mount the push-button switch and 1/4 inch phone jack with their included hex nuts. Strip 1/4 inch of insulation from the ends of the hookup wires and solder each one to a lug on the pushbutton switch and to a lug on the 1/4-inch phone jack. Inspect the soldered connections for any shorts or missing solder. Assemble the project enclosure top and bottom, using the Phillips screwdriver to tighten the screws firmly. Affix the rubber feet at each bottom corner of the project enclosure.
Turn your amp on and lower the input volume, then plug your guitar or other instrument into it. Use a standard guitar patch cord to connect your foot pedal to the pedal input jack on the amp. Raise the effects level control and input volume on the amplifier.
Step on your foot switch pedal while playing to test its effects control function.