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Selecting a decoder can be daunting if you don't know a few things about decoders. That's what this document is for - to apprise you of some simple things that will help you decide which decoder is right for you, your loco, and your way of operation.

To start with, we need to clarify a few terms.

Wired, as in "wired decoder", indicates a decoder that has wires. Typically, any wired decoder can also be purchased with an NMRA plug on the end of the wires - just add a suffix "P" to the order number.

Plug-n-Play indicates a decoder that simply plugs in for installation. The wired decoders with NMRA plug discussed above are such decoders. However, some Plug-n-Play decoders don't have wires. They have the NMRA plug right on the decoder board. These are called Direct- or Integral-Plug decoders, are the ultimate in ease of installation and neatness, and are preferable in most cases. Unfortunately, existing direct-plug decoders won't fit every loco that has an NMRA socket, which is why wired decoders with the NMRA plug are still made.

Drop-in indicates a decoder that doesn't have an NMRA plug, but is designed to replace an existing light board - simply disconnect the wires from the existing light board, remove the existing light board, drop the decoder board into the same position in the same orientation, and reconnect the wires in the same positions.

Clip-on indicates the Athearn harness that Digitrax makes. It kind of fits the drop-in description, but doesn't replace an existing board and has clips to make most connections.

When it comes right down to it, most HO-Scale locos can be fitted with almost any wired HO-Scale, and some N- and Z-Scale, decoders. The only reasons to buy anything but the lowest-cost decoder are because you want one that is smaller to fit tight areas, has more current for current-hungry locos, has more functions, has a different set of features, or is easier to install.

Size is the foremost consideration for decoder selection. It's OK for the decoder to be smaller than needed (as long as it can handle the loco's amperage needs), but you'll be hard pressed to install a decoder in a loco that's too large for it. Generally speaking, the scale indicator of the decoder indicates the scale loco it will fit in. But that doesn't mean you can't use Digitrax's Z- or N-scale decoders in HO-Scale locos, or even use Digitrax's G-scale decoder in Life-Like's HO-Scale PA that draws excessive current. As long as the decoder can handle the current needs of the loco, and it will fit in the loco, it's OK.

Current. As mentioned above, you have to be sure the decoder you're using can handle enough current for the loco. N-scale locos typically need 1/2-amp, HO anywhere from 1 to 1.5 amps, above that it's anybody's guess. There are G-Scale locos that will run on a 1.5-amp decoder, and others that require up to 5-amp decoders. The only way to know it to ascertain the current needs of the loco - whether through documentation or direct slip or stall testing.

More functions is why most manufacturers make a variety of decoders. If you have more lights or other electrical devices to control, be sure you get a decoder that has enough functions to handle all of those devices.

Different features is why some manufacturers make a variety of decoders, and why there is more than one manufacturer. If you need a feature that the TCS T1 doesn't have, find a decoder that has the feature set you want.

Easier installation is why Plug-n-Play and Drop-In decoders are made. They usually cost a little more than simple wired decoders, so you have to decide if ease of installation is worth the extra money, and has the feature set you want. However, hard-wiring a loco that is DCC-ready is not that difficult - in fact, downright easy. More about this at the end of this page.

That's decoder selection in a nutshell. But where do you start to narrow it down? The Decoder Selection by Loco pages will be the place to get your primary information. You'll look up the loco you have by manufacturer and model. There you'll find a list of decoders that will fit the loco you have. For some HO-Scale locos, there could be as many as 10 different decoders that will fit. For most other HO-Scale locos, and some other scales, there will be at least four or five decoders that will work. Your next job is to decide which of these has the mix of price, features, functions, and ease of installation to suit you best.

To start with, here's an example from the "Decoder Selection by Atlas Loco" page:

To start with, this tells us that the Atlas HO-Scale C30-7 can use the Digitrax DH165A0 or NCE-DASR.. These two boards are designed to be drop-in replacements for the light board in the top of the loco. Besides being made by two different manufacturers, there are differences in price, features, amperages, and function outputs. To see what all the differences are, check out the HO-Scale Plug-n-Play/Drop-in Comparison page.

If all you want is the cheapest decoder, for example, you can tell that at a glance from this page. But if various features are important to you, you can check the rest of the chart to find the lowest-cost decoder that has the feature set you want.

You may find features listed that you don't know about. Part of proper decoder selection is knowing what all those features are - so you can intelligently decide which features are important for you. There is a page for each feature, explaining what the feature is, what it's for, how to use it, etc. You can return to the master decoder index page to get to that feature page, or click on the decoder to get to the feature page from there.

Next the listing tells us that the TCS-DP5X and NCE-D14SRP direct plug-in decoders will work. Again, these are from two different manufacturers, and can check the differences on the comparison chart page.

Next the listing tells us that any wired decoder with or without an NMRA plug will work. That's because the light board on these locos has the NMRA socket. If you want to use a decoder with an NMRA plug, simply plug it into the NMRA socket. If you prefer to wire it up to have a lower cost and neater installation, you can do that by removing the existing board and wiring the decoder in.

We offer most of our wired decoders with and without the NMRA plug. Following is a list of wired decoders we offer with or without an NMRA plug:

Digitrax DZ143: D-DZ143
TCS T5X: TCS-T5X
TCS T4X: TCS-T4X
TCS W5X: TCS-W5X
NCE D13SR: NCE-D13SR
NCE D15SR: NCE-D15SR

These numbers are for ordering these wired decoders without the NMRA plug. We offer most of these decoders with the NMRA plug on the end of various-length wires - so the installation can be as neat as possible without having to do a custom wiring job. Refer to the decoder page listing for a list of available harness lengths and locos known to fit them. If you don't find your loco listed for any of the lengths available; open your loco, decide where the decoder will go, and measure the distance between the end of the decoder and the NMRA socket on the loco. Choose the wire length that matches or is the next length longer - or, get a plug kit with your decoder to make it any length you want.

Again, besides being made by four different manufacturers, there are differences in price, features, amperages, and function outputs. To see how each stacks up against the other, check out the HO-Scale Wired Decoder Comparison page and Small-Scale Decoder Comparison page.

While installing a wired decoder, without a plug, on a DCC-ready loco is a little more work, it's not that much more work - because all the wires are already brought to the top. To install a hard-wired decoder, all you have to do is remove the light board, identify the loco wires, then connect them to the appropriate decoder wires - using heat shrink tube to cover the solder joints. The illustration below shows how easy that is.

This is the shape and configuration of a typical Atlas light board (this is actually the top-side of a Digitrax DH150A, but will work for our illustration). All you have to do is remove the wire from terminal #1 and connect that wire to the orange decoder wire. Remove the wire from terminal #5 and connect it to the grey wire, ... and so on according to the list below. When you have two terminals with the same number, such as #4, both wires from those terminals are connected to the same decoder wire. In this case, both wires from the two #4 terminals would go to the decoder's black wire.

1 = Orange decoder wire
2 = Yellow decoder wire
4 = Black decoder wire
5 = Grey decoder wire
6 = White decoder wire
7 = Blue decoder wire
8 = Red decoder wire

So, you have a choice of three basic decoder configurations: Drop-in, NMRA plug, and hard-wired. Each has their own advantages and disadvantages.

The advantage of the Drop-ins is that they're pretty much exact replacements for the existing board - it's hard to go wrong in their installation, and you don't have to find room to put it (it simply replaces what's already there). The disadvantage is that these can be more expensive, and there's not as much variety in the way of manufacturers and features.

The advantage of the NMRA plug decoders is that they are the hands-down easiest to install - unplug the dummy plug, plug the decoder in, and you're done. The disadvantage of the NMRA plug wired decoder is that you have wires that have to be tucked away, taped down, and fitted into the loco along with the decoder - all without removing the existing board to make room for it. The best thing in this case is to order a decoder with wires as close to the correct length as you need.

The advantages of the hard-wired installation are: lower in cost than either of the other two ways, you remove the existing board so there's plenty of room for the decoder, and you can make a neater installation by clipping all the wires to the exact length needed before soldering them together. After making the connections, all you have to do is tape the decoder in place, and the wires should be laying down without hassle (that is if you've cut them to the correct lengths before soldering them together).

After you decide which configuration you want, you'll have to decide which mix of manufacturer, price, features and number of functions in that configuration fits your needs best. Once you decide that, you will know which decoder will give you the most for your money without having to rely upon others who don't know you or your needs nearly as well as you do.