I replaced some plastic wheels with metal wheels on a gondola car.'
When I put it on the track it stops everything else and cuts off.

Any ideas?

I found the problem.
I reversed the contacts on the motor.

It is dc only.

Thank you guys for your help.

It's a DC. All of my other Locomotives are moving in the proper direction (Forward for forward and reverse for reverse)

I bought a used Bachman Spectrum GP30 Locomotive.
It runs in the reverse direction when my controller (DC) is in the forward position.

What's wrong?
How do I fix it?

Thanks,
HopefulPastor