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The Digitrax RJ12 LocoNet Wiring Standard
Somewhere in the instruction manual, it says that "The RJ12 is the 6-pin version of the RJ11 connector with all pins loaded with conductors.  This is the connector that Digitrax uses for LocoNet."  At which point, your eyes start to glaze over and you go off into a trance.
Now before you go into a coma, let's back up a bit.  You're familiar with your telephone set and the cables and plugs that go into the telephone set.  On the previous page, we've shown you some of the Digitrax components that use these components.  The LocoNet consists of the same type of wires and connectors - used in your telephone system - with one very important difference.  Your telephone cables may have 2 or 4 small wires covered by that grey, black or white plastic insulation.  The Digitrax LocoNet uses components that use 6 wires. Here's what this type of cable looks like.  It's really not much different from the cable that goes into your telephone set. 

The telephone/data communications industry calls this an "RJ12 6-wire standard".  RJ12 components consist of 6-wire telephone cable, 6-wire male plugs and 6-wire female jacks.  You can have many different combinations of these components. 
  • Male plug to flat cable to male plug. 
  • Male plug to flat cable to female jack. 
  • Male plug to two female jacks - all in one plastic assembly. 
  • Female jack to female jack - all in one plastic assembly (module railroad clubs call this a gender bender). 
  • Female jack in a wallplate or two female jacks in a wallplate
  • Male plug to flat cable to two female jacks (I call this a double-female extension cord) 
This is what some of these components look like.
Two RJ12 Female Jacks in a Wallplate RJ12 Male Plug to  Flat Cable RJ12 Double-Female Extension Cord RJ12 Female-Female Gender Bender

If you have a Digitrax system, 6 wires are very important.  Anything less and it won't work. 
Here are the wiring standards, wire colours, functions, and pin-outs for the Digitrax RJ12 6-wire LocoNet.  (If you're using Lenz, Atlas, NCE, or any other system, check your user manual.) 
Note the relationship between the Pin Number, the colour of the wire inside the cable, the function, and the voltage.  If you look at the front of the male plug, you'll see that the White wire (Pin 1) is on the left, and the Blue wire (Pin 6) is on the right.  If you look at the front of the female jack, you'll see that the White wire (Pin 1) is on the right and the Blue wire (Pin 6)is on the left. 
If you visually connect the male plug to the female jack, you'll see that the white wire of the male plug connects to the white wire of the female jack, the black wire connects to the black wire, the red to the red, the green to the green, the yellow to the yellow, the blue to the blue.  This is sometimes referred to "Pin 1 to Pin 1, Pin 2 to Pin 2, Pin 3 to Pin 3, Pin 4 to Pin 4, Pin 5 to Pin 5, Pin 6 to Pin 6" wiring - or "Pin 1 to Pin 1" wiring to keep it short.  It will help in troubleshooting if you always make sure that each coloured wire connects to its own colour. 
Also note that 
  • The blue wire has the same function as the white wire - Rail Sync
  • The yellow wire has the same function as the black wire - Ground
  • The green wire has the same function as the red wire - LocoNet
So, if you happen to crimp a male plug onto the end of a cable the wrong way, it won't affect the operation of the LocoNet because the corresponding wire at the other end (blue - white, yellow - black, green - red) both have the same function.  (It's not necessary to understand what Rail Sync, Ground, or LocoNet functions are.)  However, we highly recommend that you make sure that Pin 1 is connected to Pin 1..... Pin 6 is connected to Pin 6. 
Here's that cable we showed you at the top of the page.  You'll note that, in order to keep the Pin 1 to Pin 1 orientation, we have to put a twist in the cable.  Actually what we do is crimp one of the male plugs with the tab on top of the cable and crimp the other male plug with the tab on the bottom of the cable.  The Digitrax manual shows it something like this.
We'll show you a little trick to help you keep that orientation when it comes to crimping on those male plugs. 

RJ Information for Those "Pickers of Nits"
(Skip this part if you aren't one of these people)
RJ stands for Registered Jack - as in telephone jack - as in registered with the Federal Communications Commission (FCC) by the telephone industry when plastic modular components were developed in the 1950s/60s.  Later on, as data communications technology developed, the telecommunications industry added to these standards. The RJ standards don't refer to the physical size of the male plugs or the female jack.  They refer to the way the jack is to be wired and what all of this wiring is to be used for. 
To confuse things even more, the RJ standards specify the number of cables (wires) going into the plug or jack and the number of positions available in the plug or jack to anchor these wires to.  For example, the RJ12 LocoNet plugs and jacks we use are specified as RJ12 6p6c.  That is, 6 positions are available to anchor the wires (the 6p).  And 6 cables (wires) can be wired into the plug or jack (the 6c).  And all of this wiring is to be used for a Local Area Network  (LAN) - which we call the LocoNet. 
Standard Use Pos'ns/
Authority Plug
RJH Telephone Phone Head Set 4p4c FCC 0.299" 0.355"
RJ11 Telephone Phone Single Line 6p2c FCC 0.375" 0.383"
RJ14 Telephone Phone Single Line 6p4c FCC 0.375" 0.383"
RJ12 LAN/Printer network 6p6c Industry 0.375" 0.383"
RJ25 Same as RJ12 but for stranded cable 6p6c Industry 0.375" 0.383"
RJ45 LAN/Data network 8p8c Industry 0.492" 0.459"
The columns for "Plug Width" and "Jack Width" aren't part of the standards.  To remove some confusion, I took my digital caliper and measured these plugs.  RJ11 RJ14, RJ12, and RJ25 have the same Plug and Jack Widths.  But only RJ12 and RJ25 have the number of cables/positions we need for our LocoNet. 
The Bottom Line

So what does all of this mean to you and me and our Digitrax Loconet system?  We have to make sure that we use a plug/jack that is about 0.375"/0.383" wide and has a 6p6c configuration - ie it takes 6-wires.  The only jacks/ plugs/ components that fit the bill are the RJ12 and RJ25. 

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