To get to the tabs on the trucks it's not necessary to dismantle the truck itself, or remove it from the chassis/frame. Removing the shell will give you access. Depending on the model, it will, if a bluebox, be a single wire soldered to a brass tab (the other electrical contact is via the frame) Later DCC ready locos will have a tab on each side of the truck sticking up. If the wire soldered to it has broken, try and melt the solder and pull it out to clear the little hole it passes through. You may need to redrill it anyway to clear it. Clean the surface of the tab with a small file or sandpaper before resoldering. Don't linger too long on it with the iron or you could melt the plastic of the truck. (the reason for making it clean). The other exception to the double tab is the early DCC ready types where they still only had 1 tab sticking up and relied on the contact of truck to frame for the other, On those, the motor was insulated from the chassis, but received power from it by a wire attached to it with a screw.