While recently installing my first decoders to some Kato F3 units, I found myself scratching my head over what to do with the B unit decoder boards. In the Katos (and likely others), the mechanism has the same engineer seat, etc. as the A units, so the LEDs can be formed to fit rather than snipping them off. I went ahead and did that, so I now have B units with interior lighting. Obviously not useful for much, but I have found it a good way to identify which unit is which (by toggling the headlight) and to verify that the decoder is "on line." What do the rest of you do?