I often rewire the Hornby connector when installing decoders, quite frequently the wire isn't long enough to to reach part of my installation. Occasionally you get one that really sucks, and gives continual shorts. When that occurs I simply replace it. Their cheap and available from model spares Burnley for a few pennies. Your short may lay somewhere else within the loco it might be that when wiring up Hornby crossed wires it's easy to do as both of wires are a helpful shade of black. So track them back and make sure it isn't a wiring fault. When you do find the fault please seal your rework with shrink tube, I'm coming across lots of installations where insulation tape has been used, and that's not good practice. It eventually unravels and causes a short or a blown decoder. You can buy very nice thin wire 0.7 mm in packs from All Components, get some thin shrink tube as well (1.20) and do a nice neat job.
Originally I used to totally replace the connector and epoxy in a 3mm brass screw remove all the gubins from the connector and use that and the link between tender and loco, the pick-up wires were connected with a simple two plug connector also available from all components. But that's a lot of work, and folks don't like it because you've changed the original (crap design). It is certainly more reliable and looks better too.
Originally I used to totally replace the connector and epoxy in a 3mm brass screw remove all the gubins from the connector and use that and the link between tender and loco, the pick-up wires were connected with a simple two plug connector also available from all components. But that's a lot of work, and folks don't like it because you've changed the original (crap design). It is certainly more reliable and looks better too.

