The purpose of this device is to change over the slider that draws the current at the time you change direction in your railcar. We do this so that the front slider is always the source of current for the loco. Why? For most layouts without a booster or current sensing s88s (e.g. Viessmann 5233) and railcars with only one motor (sometimes) it probably does not matter. But in those other instances, where it does matter, you need one of these units if you are going to change decoders.

It looks like this.



The spikes in the middle of the board can hold a 21 pin mLD3 or mSD3. When you use a mSD3 you can plug the speaker into the socket at the lower edge of the board.

Unlike installing a decoder, this is a nightmare. Mainly, because the instructions are so poor and the board itself has no wires or additional pads for lights.

Here is an example of the problem with the instructions:



What the above nonsense means in real English is that you open up the Marklin Decoder Programmer on your PC (You must have the stick, with the decoder, installed into your PC's USB port). After you have read in the settings (using the Read out Decoder option from the Decoder drop-down on the main menu), you select the spanner on the lower Function section of the screen to see the screen below.

Click the + next to special functions and add the "ALWAYS" function then the green tick.. Click on the newly added "Always" then click on the + next to outputs and add output 3 and 4.



Click on each output to set the direction.



It took me ages to figure this out for myself. I hope it is useful for the next poor soul who buys one of these things.

Another thing that could have been a huge improvement would have been a socket to add a 60974 Buffer Capacitor.

One day, I will look at the ESU 51966. At least their manuals seem to be better.

My ratings (max five *):
Documentation *
Ease of installation **
Fit for purpose **** (does what it claims, after you engage in some Jedi mind reading to translate the "English?" pages in the manual.)

I recently did an upgrade using the 60973 and an mSD3, and noticed that the AUX 1 and 2 are incorrectly labelled on the board, they are swapped. But it's correctly in the manual.

otherwise, it worked as intended, and I agree that the documentation could have been better and a susi socket would have been nice. but it worked well just soldering the 60974 to the free pads.

another thing is, that it is possible to add logic to the relay switching, so you can choose to disable the relay switching and drive a locomotive unit alone in both directions. eg on the ICE 1/2 with one motor. (as long as the locomotive is put in forward before you disconnect the train.)