The foot pedal no longer operates when plugged into the fill jack

Thre is a sustain pedal jack next to the foot switch jack. The pedals used are different. The foot switch is a latching switch, the sustain pedal is a momentary.

Does your M foot switch work on the Fender? If you know how to use a multimeter you could check continuity by putting meter leads on plug of M foot switch(1 on tip, 1 on sleeve ) You should see a change in the multi meter when you depress switch. If so switch is good. Another easy test is with cap off a spare 1/4 plug -plug it in to foot switch jack.put a alligator or some such metal clip or wire and join(called short or shorting) the two inputs . If connecting and unconnecting results in switching then the foot switch is suspect. One fairly common thing is that foot switch and input jack are often sautered straight to a circuit board to save $ on production cost. Used to be all point to point where a wire was attached to 1/4" input and then wire went to circuit board or tubes. The wire has give, but not so with direct wiring to board. So the nut holding the 1/4" amp input gets loose(doesn't have to be loose for the following to happen) and a pull on the chord causes a break in the soldier and thus a break in the sound chain. Sometimes it will work intermittingly by putting a little pressure left, right, up or down on the plugged in plug. If so, it's the input jacks connection to the amp. If not it still could be that because putting pressure on plug may not be sufficient to affect a temporary reconnection. Since switch(the new one you made)works on Fender, but not Marshall I suspect the jack or foot switch circuitry past the input jack. If using some of the above the above tests leads you that direction,remove housing(unplug a/c power 1st ) inspect jack,wiggle it slightly see or feel a break then resodier from back side. You should be able to use the soldier already present without adding extra.

every sustain pedal got different polarity.. normally just go to global setting on your keyboard and change damper polarity setting to plus or minus (select which one work with your sustain padle).

Make sure you are NOT using a TRS (stereo or three conductor cable) type cable. PLugging into the input should turn the pedal ON, not off. The switch on the jack may be broken or soldering to the circuit board may be broken OR worst case, there is a crack in the circuit board.

Likelythe connections and or jack for the foot pedal control are making poor contact resulting in triggering these other modes. If not using the foot switch, probablly the problem is poor contact of the switches on the jack.

This is likely a bad jack for the foot pedal, or a problem with the pedal and cable. The jacks are junk and even with the pedal unplugged the switch contacts on this jack will vibrate and cause your problem.

In refering to the schematic i find that the MOST probable cause would be a bad switch contact on the jack the pedal plugs into. There is a normally closed contact that passes the select signal within the unit to the control circuit. If the contact vibrates open, then the unit will switch. These jacks are a pile of.... prone to failure if you use them very much. With the pedal plugged in the switch is no longer in the circuit and control is solidly by the pedal.

If you remove the amp from the cabinet you can probably bend the spring contact to temporarily fix the problem, however, use that jack a bit and the problem will come back. You could cobble a good quality Switchcraft jack with switch as a replacement and add pigtail wires to the circuitry for a little better reliability.

Try testing your switch for function by testing it with a volt ohm meter to make sure the cord and switch are functional. In this case if it is the recommended foot switch it will be momentary on or off. That is if you are using your meter to test across the plug, when you press down you should have no resistance displayed if there was resistance when you connected the probes or resistance displayed if there was none when you originally connected the probes. If the switch is good, your problem is internal to the keyboard and you will have to troubleshoot the circuit on the board. Another possibility is the solder joint has failed where the sustain pedal jack is mounted or the jack itself has failed.

Replace the switch. You gave no make/model number for your amp but if it has a jack for foot pedal operation of clean/dist function then try that. (on most amps) it will switch in spite of a bad front panel switch.

Run a jack from your guitar to Input R Mono on the pedal.
Run a jack from Output R Mono on the pedal to the input of your amplifier.
There is a switch for guitar or Bass. Put the swich on guitar
You do not need a preamp to use this pedal.
Hope this helps,
Maxx.