On some other forums, I've seen posts that say you need small, specially built DCC boards to convert DC locos to DCC. It's can't be done ANY other way. That's a bunch of BS! Here are pics of conversions I did with two cheap Lenz decoders salvaged from a couple of Bachmann locos. I put one of the decoders into a Proto 2000 E7 and the other went into a BB Athearn F7-A.
First the E7. The light board was removed and the decoder was hard-wired into the wire harness. The lights were changed out with 14v replacements and get their power directly from the track. The decoder controls motor functions only. After being wired in, a strip of masking tape was placed on the non-component side of the board as insulation. The board was then pressed down onto the top of the chassis and secured in place with strips of masking tape.
Now to the Athearn F7. The motor was isolated by removing the grounding tabs from the bottom of the motor and a strip of electrical tape placed in the motor well. A ground wire pigtail was soldered to the motors ground strip. All previous wiring was removed from the top of the motor (pick-up wires from trucks and wire to headlight) and a pigtail soldered to the top of the motor. The existing pick-up wires from the trucks were soldered to the + input pads on the decoder. A ground wire was soldered to the old light bracket base on the loco frame with the other end being soldered to the - input pad on the decoder. Wires were then soldered to the + and - motor output pads and soldered to the top and bottom of the motor respectively. For lighting, I used the existing yellow-gold LED on the decoder. I put a strip of masking tape on the non-component side of the decoder, placed the decoder atop the motor and used one strip of masking tape to secure it in place. In this loco, the decoder controls motor function and lighting.
First the E7. The light board was removed and the decoder was hard-wired into the wire harness. The lights were changed out with 14v replacements and get their power directly from the track. The decoder controls motor functions only. After being wired in, a strip of masking tape was placed on the non-component side of the board as insulation. The board was then pressed down onto the top of the chassis and secured in place with strips of masking tape.
Now to the Athearn F7. The motor was isolated by removing the grounding tabs from the bottom of the motor and a strip of electrical tape placed in the motor well. A ground wire pigtail was soldered to the motors ground strip. All previous wiring was removed from the top of the motor (pick-up wires from trucks and wire to headlight) and a pigtail soldered to the top of the motor. The existing pick-up wires from the trucks were soldered to the + input pads on the decoder. A ground wire was soldered to the old light bracket base on the loco frame with the other end being soldered to the - input pad on the decoder. Wires were then soldered to the + and - motor output pads and soldered to the top and bottom of the motor respectively. For lighting, I used the existing yellow-gold LED on the decoder. I put a strip of masking tape on the non-component side of the decoder, placed the decoder atop the motor and used one strip of masking tape to secure it in place. In this loco, the decoder controls motor function and lighting.