spot lights and dc

[jmmrlm]

I have miniatronics rail yard spot lights whose instructions say to connect the cable with the diode to the positive connection of the DC output of a transformer .

The power source I am using is the MRC Railpower 1300 that has both DC and AC output terminals. But the DC are not marked positive or negative.

How would I know which is the positive terminal of the DC output on the MRC 1300 in order to follow the Spot light instructions?

[Ton N]

Depends on how you turn the knob.
backwards is always the reversed polarity of forwards.
But if there is a diode in your circuit it will stop the wrong polarity because a diode is a one way valve for DC

Ton

[rich1998]

The DC output is usually not marked. Depends on forward or reverse selection.
You can also use a DC meter to determine.

Rich

[Len]

You would do better to find a 'wall wart' transformer of the correct voltage to use for the spotlight, rather than the 1300 with it's variable DC output.

Len

[jward]

Since the diode will convert Ac to the proper polarity DC why not just use the AC terminals?