Nicely done Jonathan.

If the loco you are trying to run is HO or N scale you will need a DC transformer(power pack)

O scale uses an AC out put transformer.

Look for a power pack that says; DC output-16 volts or so.

When you removed the rubber (traction tire) did you have that axle out of the truck? May be that you put it in backwards.

Sometimes it does make a difference how the axle goes in. If you reversed it, you now have a short.

Pretty neat video.

I have repaired many Bachmann locos using Loctite Professional strength super glue. I know of no failures.

Just be sure everything is very clean first.

If you're using a 'Scotchlok' type of connector where you insert the wires and squeeze a disc down to make the connection; you don't need to strip the wires.

That style of connector is an "IDC" type.  (insulation displacement connector)

OK Quentin,  you had good advice already and I got to wondering if some basic problem could have been overlooked.

Any chance one of the trucks is binding or a bit too tight?

Have you checked to be sure that the problem car has all its wheel sets in gauge?

Microscale makes a product called 'Liqui-tape'.

It remains sticky so the rails can be removed in the future if necessary.