Can't see any such asset on the DLS. If that asset was supplied by a third party then your enquiries should be directed to them.
Have you confirmed that the vehicle mesh has a
a.pant0 attachment point? That is the correct way to connect a pantograph and ensure that it works. You might be able to get it to work using a mesh table entry, but it's still going to need an attachment point, and you will need a script to activate the animation. But in any case it should not be under default: that will already be there for the main mesh.
Start with the standard pantograph setup - a proper attachment point and the
pantograph tag. Only consider a mesh table entry if you can't get that to work.