Won't run after putting in new batteries. - Cars & Trucks

Batteries in what? Make sure the “+” is connected to red or positive if you installing smaller batteries like remotes etc. the bump is the “+” positive and watch batteries is the side that is smaller and has a rim around it.

Negative is the”-“ ground or black wire,
The smooth side on watch batteries the side that goes on the doing on cylinder style batteries and in some cases it will be a braided or uncovered connector. Bare wire terminal. Test you battery in another item known to work. To verify it has charge. If your still not getting power update your question with more information or take it in for service .

Check for dirty contact points, clean, and retry.