The yellow wire pops up next to the gun motor and is just waving in thin air, the black and red wires went into the tank hull and are also waving in thin air, it looks like they were never connected up as there's no sign of solder on them. The yellow wire might have come off the motor, which would explain why the gun does not work. You know how these things are put together... might have been fine when it left the factory and then just come off due to a poor solder join and some vibration.

To be honest I'm not too bothered that it's in a bit of a state, there is really only one part broken (one suspension mount point) which can be fixed, and the tank runs fine without it for the time being anyway.

Judging by all the carpet fibres I'd say this has been the toy of some kids / big kids for indoor use only, the seller had two identical tanks for sale - this was the damaged one, the other made about 150% more in a separate auction. It did come with metal idler wheels already fitted though!