Since I have now built a pile of k83 modules (actually Viessmann 5211) I need to test them. Each one has 12 outputs to be tested, I decided that a small plug-in module was in order.The module tests three plugs at a time, allowing all four output pairs to be tested in turn. I took a piece of plywood, screwed three Märklin plugs into it and connected them up to two LEDs and a 1.5K Ohm resistor.
This allows me to insert the tester into a k83 and when the ports are activated the red and green LEDs flash accordingly providing a clear indication that the module and address selection etc. is working!
Update 2017
This little tester has proven to be invaluable over the years, and I sometimes still use it 10 years later if I need to determine if some accessory has a wiring problem or if the k83 type module has a problem.I also have k83/k84 testing capabilities through the main program and my browser on my phone