Confused!

I have a few cheap-end RC cars and one cheap helicopter. I work on computers all the time. Here is the issue I'm running into however;

I work cleaning apartments in between tenants for a living. I found a 1:10 scale car in one of these units and brought it home. It doesn't have the top car part, just the base with the wheels, motors, etc. From the markings and labels on the bottom I think it was a Crysler Hemi 300. The remote works, the battery works, the front steering wheels work from the remote. The MOTOR for the back driving wheels works when hooked -directly- to a power source (the battery). The wires coming off of the card towards the back motor have power when hooked to a meter (though I don't know -exactly- how much since my meter is messed up, just that it moves the needle). BUT with the wires hooked into the motor, I get nothing. I can't figure out where the problem could be after reaching the conclusions I've reached. Any amount of help would be terrific.

Thanks in advance,
Lincthra