Help understanding locomotive wiring

[victortorgrimson]

Hi,

My 8 year old twins and I are starting to work on my Dad's old model railroad. I was considering trying to convert some of his old DC locomotives to DCC. I would guess this locomotive is about 50 to 65 years old. It runs well. I recall my Dad put new motors in many of his locomotive about 20 to 30 years ago.
I opened it up and I'm trying to understand the wiring of it and the implications for converting it to DCC. I'm hoping you might be able to help me with a few newbie questions:
1) The two gray wires from the pick-ups and the two yellow wires to the motor appear to all four be soldered to each other. Is that unusual, and could I just disconnect them and add the decoder at that point?
2) In the middle foreground of the picture there is another wire that I guess is going from the motor to the bottom of the frame. What is that for? Is the black and pink on it a resistor?
3) The headlight has one wire going to the wire I mentioned in #2 and another going to the frame. So I guess the headlight must be running its circuit through the frame? Should I remove the wire in #2, remove both of the headlight wires, and just wire an LED into the decoder?
4) Does it seem likely that the motor is still not going to be isolated from the frame, which I gather would be a problem for DCC?

Thank you for any help with my newbie questions! I've searched a lot of websites and videos but haven't spotted this scenario.

Victor

 

[kjd]

It looks like an Athearn F7. The frame is half the electrical circuit. I don't know about the lighting, I didn't ever figure out DC constant lighting. You don't need it where you are going, DCC makes lighting pretty easy. The motor is grounded to the frame but should be easy to isolate since it has two tabs for connections. I would remove all the wiring and start fresh. Connect the tabs on the trucks with a jumper then the red decoder wire attaches to the tabs sticking up from the trucks. The black goes to the frame. The orange and gray go to the motor but it depends on how the motor is installed. If they are attached and the loco runs the wrong way compared to the lights, switch them. The blue and white go to the front headlight, blue is + and white is -. Blue and yellow go to the rear light. If using LEDs and the decoder doesn't have LED outputs add a 1k resistor in series with each LED.

 

[dennis461]

I am converting one of those this week!
Here is the best instructions for that brand loco.

Also, do you have the giant weight that goes inside?

Weight in older athearn F7

I'm upgrading my older athearn F7's to DCC. I put the decoder on top of the motor, but the weight will not fit over it. I tried milling some of the metal but I cannot get a good cleareance. Do I need to put the weight back in? I'm affraid of loosing traction.

model-railroad-hobbyist.com

 

[trailrider]

You can use sandpaper or emeryboard to clean/roughen the solder tabs. If you do use the wire brush in a rotary tool, BE SURE TO WEAR EYE PROTECTION! If the engine does have a weight you may need to remove some material to have room for it inside the shell. If not, you can purchase stick-on weights to place in convenient areas, being sure they don't interfere with the drive shafts, flywheels or truck towers. I would test the installation before and after replacing the shell on the chassis. Also, some other decoders may have keep-alive capacitors available. These are handy for short wheelbase locomotives that may stall over insulated crossovers, turnout frogs, etc.

 

[victortorgrimson]

Thank you all so much. All of your responses are incredibly helpful!

 

[D&J RailRoad]

The most important thing is to isolate the motor from the frame when installing the decoder, otherwise you'll burn up your decoder before the loco even starts to roll.

 

[J.Albert]

Sometimes the old ones are just so much work, that it might be easier to "leave them be" (or perhaps place them somewhere on the layout in stationary "display only" service) -- and get something newer that will be easier to convert (or may already have dcc and sound installed).