As I mentioned previously, my Athearn switchers have all been remotored. However, the modifications to the trucks are the same, so here are some pictures to clarify things. (Hopefully!
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This is an Athearn switcher: you can see how the strap that sticks up from the truck has been cut down - this eliminates any chance that part of it will inadvertently rub on the motor, flywheels (mine have been removed), or inside of the bodyshell. On this loco, it also helps to avoid contact with the lead weights that are secured to the inside of the bodyshell.
Here's a view with the driveshaft removed: the black wire is soldered to the stub of the former strap, while the red wire is soldered to the other, normally unseen contact strap. The truck retaining set-up is a bit different on these switchers than that used on the geeps, but the main thing to remember is to keep the solder build-up and the wire away from the area around the hole in the strap that the nub on the frame seats into.
Another view of the wire connections. Here, and in the shot above, you can see the rust on the flat strap to which the red wire is soldered, one of the reasons why the strap system is not very reliable.
The set-up with the circuit board, rail joiners and bits of rail soldered to the ends of the wires was installed to permit easy change-out of the trucks or motor, without having to unsolder anything, and was installed before the current trucks were acquired. This would probably make it easy to convert these locos to DCC, too, although that is not my intention.
On a loco with its original motor, the red wire (from both trucks) would connect to the copper strip on the bottom of the motor. To make this connection, it's best to remove the motor from the frame, then remove the copper strip from the motor: it simply pries off, but be careful, as it retains a spring which holds the lower motor brush in place - don't lose either! The black wires connect to the top copper strip on the motor - remove and discard the long steel strap, which will reveal the copper strip. Remove it as you did the bottom one - careful with the spring and brush on this one too! Removing these copper strips before soldering avoids heat damage to the motor, springs, and brushes and also makes soldering easier, as there's nothing else to heat except the strips.
Hope this will help to improve the performance of your Athearn locos.
Wayne
especially the joiner and rails! 
