Fortified by a number of successful decoder installations, I started looking around for the next project. In my collection I have a number of older locomotives that run well on the DC side of my layout, so I should be able to find another one to install a decoder in. Remember that if your subject locomotive does NOT run well on DC power, it REALLY won’t run well on DCC! I decided it was time for a larger locomotive to go digital. The next project was a nice older N-Scale LifeLike SD7 diesel locomotive. This should be fun!

Just as with the other locomotive decoder projects I have done, the first thing to do is pry off the shell to see what is inside. So far I’ve been lucky and come up units that lend themselves well for conversion to DCC. Not so with all older units! Anyway, when you pry off the shell, be gentle. The plastic the shell is made of is very thin and fragile. Not only that, but this type of older frame and motor mount doesn’t have much “substance” to it. (The newer units have a lot more to them) Be careful NOT to bend the frame when you take it out of the body!

Now that the locomotive is completely disassembled, this project looks like it should be easy. The wires for power pick-ups and motor contacts are easily accessed and isolated. The headlight should also prove to be easily wired in (This unit didn’t have a rear light) and if I simply remove the back weight there’s even plenty of room for the decoder. This installation might be the easiest one yet!

It’s time to isolate the motor and remove all the old contacts. Take a few moments and find were everything connects. The track contacts, the two motor contacts and the two light contacts. I noticed one small problem that I will have to pay attention to.

You might remember from the other articles that I have talked about the NMRA Standards that cover decoder installation? With the way they have the motor power contacts attached to the bottom of this locomotive, it will be hard to figure out how to wire in the decoder. More on that later. This unit was made long before these standards were established, and makes a wonderful case of why we need standards in the first place.

Removing most of the old contacts proves to be easy. Just take your preheated soldering iron, clean the tip EVERY time before you touch something, add a little solder to the tip and place it on the joint you want to take apart. The little drop of solder on the tip makes the other solder on the contact melt much faster. Be VERY careful not to get the contact too hot. If you melt or warp the frame, this unit will never work again!

The one “tricky” thing you have to do with this decoder instillation is isolate the lower motor power connection. Remember that ALL the old contact points must be isolated for the new DCC to work! Too accomplish isolating the lower motor contact, simply take your rotary tool with a grinder tip and remove that little section of metal running to the side power strip. Make sure you remove all the connection or you will burn out the decoder!

It’s time to move on to the decoder. Personally, I like to use the Train Control Systems “M1” decoder for most of my projects. Not only is it one of the smallest units available, but also they have a wonderful “no questions asked” guarantee. You kill the decoder with your installation; they give you a new one. (Can you hear the “voice of experience” here?) You can’t get a better guarantee that that! For more complex applications, I use other decoders, but for the most part the M1 is for me.

Now is the time to make sure the decoder will fit in the space allowed. I used a little bit of foam double-sided tape and placed it on the rear gearbox. I ended up having to lightly sand off the top of the gearbox to get the tape to stick. It seems I was a bit over zealot with the lubrication, and I had to clean the top off to get the tape to work. I then separated out the track power pickup wires and the top motor wire and moved them to the side. The rest of the wires I ran forward and taped them to the top of the motor.

Take a few moments to make sure the decoder is positioned correctly. Hold up the removed weight and compare where the decoder is now sitting. Is the decoder within the profile of the weight? Front, back and to the sides? It’s MUCH easier to make adjustments now rather than later!

On to the NMRA Standards Chart to figure out which wire goes where. All decoders have the same colored wires going to the same places. Some decoders have MORE wires than others, but they are just for more functions. The basic wires are all the same colors, no matter the brand. The problem remains with that old style motor. Which wire goes where? More on that later. After you figure out where the wires go, cut them to length with a little to spare.

Strip the ends of the decoder wires a very short distance. When you solder, as the wire heats up the insulation pulls back to expose more bare wire, which can cause problems later. I then “tin” all of the wires. “Tinning” is when you pre-solder all the ends. This makes it MUCH easier to solder them later to the contacts.

It’s time to start hooking things up. We now need to solder all the wires to the correct places. Be careful with the heat, as we don’t want to melt anything! I start by connecting the red and black wires to the siderail track pickup strips (as per the NMRA Standards Chart), and then the wire to the top of the motor. After soldering, carefully move the wires around so they aren’t touching anything moving. We don’t want any problems to show up later!

Now comes the light. The NMRA Standards state that the blue wire is the hot side, and the yellow and white wires are the directional leads for the front and rear lights. Sense I don’t want a rear light as the original locomotive didn’t have one, (But you certainly could add one) I’ll only need the blue and the white wires. With this type of bulb, you don’t need to worry about which wire from the light goes to what color wire from the decoder. With an LED bulb, you do. If you connect an LED up backwards, you’ll burn it out RIGHT NOW! (There is that old “voice of experience” again)

I use “shrink tubing” on all the solder joints I can. I just love this stuff! I always try to keep the wire leads as short as possible. That way, you have less wire to deal with when you put the shell back on. Once again, be VERY careful with heating the “shrink tubing”. You don’t want to wreck the unit this late in the game!

Almost done! The last thing I had to do was make sure the loose wires did not get into the moving parts of the motor and gears. Did this installation work?? You bet! But………. It ran BACKWARDS! With those darn old motors you have a 50/50 chance of getting the wires on the correct sides. I simply moved the two motor wires around and it worked in the correct direction. This unit runs even better on DCC than it ever did on DC.

Another success! At this rate, I won’t have any DC locomotives left. Actually, that would be OK, as these digital decoders will run the locomotive on a DCC track or on a DC track. Some say you can run a DC locomotive on a DCC track by using something called “0-Addressing”. But I strongly don’t recommend it. I don’t know about you, but I don’t want to replace locomotives if I don’t have to.