I agree that it is better to build your own external ones. The ones from Lionel use about 20 gauge wire. You can build them more robust than that.
As for how you wire the external box, you can have the diodes normally in circuit and take them out of the circuit when you push the button. For me, this always speeds up the trains as it appears to me that I am adding 3.5 volts or so back into the circuit. If I wire them so that the diodes are normally out of the circuit and I add them in when the button is pushed, it seems that I am removing 3.5 V or so and the trains slow down. I chose the slow the trains down approach as there are places on my layout that I don't want to speed up the trains.
I have also wondered about the external xener diode approach. These diodes seem to get high marks for not affecting train speed. I would love to see an external approach using these.
Denny
