The bottom line is, do not use a pot to control a motor directly, simple PWM/Mosfet circuits are cheap.

I agree 100%.

As for asking

So how big is the motor?
How much current does it draw?
What is the capacity of your battery in volts and amp hours?
What gauge wiring are you using?
How are you wiring it up? (wire schematic needed)

This isn't in preparation for taking the "POT" approach but rather to understand the parameters we're working with so we can make a good recommendation as to a viable and stout solution to the TS needs.

 

It is also entirely possible that the current is not great enough to provide an indication on the meter. That happens quite a bit. I have a power supply with digital meters that only read amps, tenths of amps, and hundredths of amps. A 5 milliamp draw will not register at all. But it will light an LED connected to the supply.

Was pointing out the reason for the failure and not making the suggestion of using a pot to control motor speed.

That's either because you already burned out the pot OR you've wired it wrong.