The underside of the tender showing the coupling. The spring is not there to act as a spring. It
is there to make contact with the base of the weight at one end and
with the screw in the coupling at the other.
Note the plastic insulation on the tender axles at the hub of the
wheels on the right hand side of the tender (right hand side of the
upside down photo). This plastic hub isolates the right side wheels
from the left. It is very important that you are aware that
the wheels have to be fitted the correct way round. Normally
the left (negative) side is connected to the chassis through the
axles. So the insulation goes on the right (positive) side of
For this particular tender, it doesn't matter - as the axles are not
connected to the chassis, and electrical pickup is from the top of
the flange of the wheels. But get into the habit of checking.
If. for example, you put the bogey wheels in the wrong way round,
you will get a direct short across the track, the transformer will
cut out and the train will not run.