In the thread about 3071 in the H0-forum I promised to report about the conversion of my 3071 (and 4071).
First I opened the control car (the rear coach if the engine is pulling the train). The control car also has a slider, which is in use if the train is pushed in stead of pulled. The red lights are always on, as expected. If the control car is in front, the yellow lights overpower the red ones so you hardly see them.

I had decided to add a resistor to protect the rear light from the higher digital voltage; I found a 12 Ohm resistor and soldered in between the rear light and the slider. The resistance of the rear light appears to be some 45-50 Ohms, so the 12 Ohms should be OK to limit the voltage over the lamp to 16. The other red wire goes to the motorcar to feed the engine if the control car is in front; the yellow wire is for the headlight of the control car..

The dimming effect of the resistor is not as high as I wanted, so maybe I'll add another.
Then came the more interesting part. First opening the motorcar:

The analog controller of direction, lights and sliders is complicated:


The decoder (a 66032 from M*) is connected; I fixed it to the chassis with Velcro.


Ofcourse the leads from the decoder have to be shortenend. I will do this after I receive the later mentioned bi-stabile relay I have on order at Conrad. This relay was ment for switching the power in to the slider in front of the train, depending direction of travel.
Then it was time for a test run. I made the mistake to connect the controlcar at first ride. Apparently I put the connector upside down, because when I switched the power on, the decoder made a loud buzz and a little cloud of smoke. The decoder output for the front light at the controlcar must have gotten connected to the slider of the control car, which is on the digital power from the track (the other lead through the train was not yet connected).
Then I tried the loc on itself, and then the loose connector touched ground, gave a small spark and that was it. [:I][:(!][xx(]
But after all the only damage is to the switching of the lights function. Lights still work, but are always on (both sides). Rest of the decoder works fine. At the time the train is running with yellow lights in the motorcar and red lights in the control car. Running it the other way is possible, but leads to derailments.
So my plan is now to add a bi-stabile relay, connected to the motor-controls (green and blue wire from the decoder) to switch headlight from front to rear. Maybe I'll also connect the red rear lights accordingly. The power for these lights will be direct from slider, not from the decoder. I think it will also be possible to effectuate changing from one slider to the other this way.


Evaluating this conversion I think it is not a good idea to use the leads through the train for power which comes from the decoder. To put the train together, you have to connect three connectors between the coaches and - as appeared - it is easy to connect them the wrong way. In analog service this is no problem, the only thing that will happen is probably that the rear headlight and slider won't work but in digital operation it is fatal for the decoder.
Hope this helpes those of you who are planning the same conversion.
Regards, Henk.