I thought the PDS controller (Curtis 1206MX) was to only one with M- labeled A1.
Oh well, I'm here to learn also.
I believe M- stands for Motor Negative, which typically connects to the motor's A1 (Armature-1) stud.
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Anyway, in a DCS cart, the solenoid gets B+ from the external control circuit.
Red highlighted circuit on attached schematic.
When the pedal switch is closed, B+ is applied to Pin-5 on the controller and the controller then connects B- to the solenoid.
If the solenoid does not de-energize when the pedal is lifted, either the pedal switch is sticking closed or the controller is bad.
You said the voltage on pin-5 came and went as the pedal was pushed and released, so that leaves the controller being bad.
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Perhaps you can get a warranty replacement from wherever you got the "new" DCS controller you installed, but if you can't, or when the replacement DCS controller fails, replace it with a Alltrax DCX400.
DCS controllers (Curtis 1206SX) don't have low voltage protection and are high failure items. The DCX and similar aftermarket controllers aren't afflicted with the same weakness.