Cars running backwards

[Bobets20]

I'm having trouble with a few of my slots going in the opposite direction On an analogue track

I have 5 scalextric slots (2 of them are Holden commodores that came with the analogue Supercars set) and an SCX. 
the 2 Holdens and the SCX run in the opposite direction after I added additional track.

has anyone encountered this problem before? How did you rectify it?

thanks

[Andy P.]

"after add(ing) additonal track"

So what kind of track did you add?

Does everthing work when you take the track back out?

Are you mixing analog and digital?

If the cars are used it is entirely possible that the motors are wired the other way round or that the rear axle has been flipped over.

Normally  I would say use a 9 volt baattery, noting the plus and minus sides and test if they are simply wird differently but "additional track" comment makes me wonder...