I am in the process of equipping my diesel locomotives and passenger cars with power connectors.  This is not a new or unique idea.  It has been used for many years and there have been quite a few magazine articles written on the subject.  By connecting power between cars or Locomotives, the modeler will receive several benefits, especially those of us that run out door and fight the dirty track problem.  The benefits of this technique are: passenger cars with track powered lighting will experience little or no flickering with power pickup shared the length of the rain, multi-unit (mu'd) engine lashups will experience less power pickup problems such as bucking and stalling when hitting sections of dirty track.  I have mentioned in previous articles that steam locomotives, especially an 0-4-0 with a short wheelbase, will definitely benefit from using the eight wheels on the tender for additional power pickup.  Remember, the more points for power pick-pickup the smoother your train operation will be.  I could eliminate all this work by converting to battery power, but I run multiple engines with a lot of lights and smoke and sound.  Batteries just would not last in this type of railroading.
       I have standardized on "D" type mini-connectors  which are available through electronic supply stores.  A catalogue can be obtained from Digi-key on the internet at or you can call them at 1-800-digi-key.  They are real quick to ship and their prices are good.  The plugs come in male and female and both are installed at each end of the diesel or car so that if the unit is turned around, the contacts will still line up.  The wires are simply soldered to the lugs that are connected to the power pick-ups on the trucks. 
       To install these connectors; use 20 or 22 ga black wire (use fairly stiff wire) and 3/32" black heat shrink tubing.  To assemble the connector, solder a length of wire to each contact.  Cut a 1" length of heat shrink tubing and cover the female connecor all the way to the end.  Shrink this tubing using a hair dryer or butane lighter.  Insert the male connector into the female connector and slip heat shrink over the male connector until the tip is covered.  Shrink only that portion that covers the back portion of the male half, leave the par that overlaps the female contact unshrunk.  Unhook the connectors and rim the heat shrink on the male end even with the contact.  Trim the wires and solder to the correct points on your cars or locomotives.  A small blacktie-wrap should be used to secure the wires on either side of the truck mounted coupler. 
       This technique will provide you with excellent elecrical conductivity through the length of your passenger rain or multiple engine lash-up.  The connectors also look like brake lines or mu hoses and do not detract from the appearance of the train.