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What An RJ12 Telco Jack Look Like
(But you can skip this part if you want to.)
I like to take things apart just to see what they look like inside.  Here's what the various parts of a female RJ12 telco jack looks like. 

At the top of the above photo, we have the faceplate for our telco jacks - in this case it's a dual faceplate for two jacks.  Below that we have a plastic body with 6 screws - for the 6 wires.  Below the plastic body we have a series of wires with spade terminals on one end (which fit under the 6 screws of the plastic assembly), and some bent phosphor-bronze spring wire that is crimped onto the other end of each wire.  The phosphor bronze spring-wire fits into a small plastic assembly and the assembly snaps into slots in the bottom of the plastic body.  In the bottom of the photo, we've taken out the phosphor-bronze/ coloured wires/ spade terminals and straightened out the phosphor-bronze spring wires.  That's all there is to an RJ12 telco jack. 

RJ45 versus RJ12 - A Caution
RJ45 looks the same as RJ12 except for two very important differences. 
  • RJ45 is an 8-wire standard. 
  • The plugs and jacks are wider than their RJ12 counterparts - 7/16"vs 3/8". 
  • An RJ45 male plug won't fit into an RJ12 female jack. 
  • But an RJ12 male plug will fit into an RJ45 female jack. 
  • A lot of RJ12 female jacks are really RJ45 jacks in disguise!  The faceplate is an RJ12 faceplate but the jack part is really an RJ45 female jack. 
  • An RJ12 male plug (like the one on the end of your throttle) will probably get stuck in this RJ45 female jack.  It may also short across the pins and cause you lots of grief!
  • How can you identify an RJ45 female jack?  Look inside the female jack from the front.  On the left side of the jack, you'll see a little notch.  The notch identifies it as an RJ45 female jack. 
  • The RJ45 female jack is also wider than the RJ12, although that may not be readily apparent at a quick glance. 
  • How do you convert an RJ45 female jack into an RJ12 female Jack?  Simple!  Snap the female jack from the faceplate (a good twist-bend-and-pull is required).  Then ACC a short piece of 0.040"x 0.250" styrene on each side of the RJ45 female jack.  This narrows the width of the RJ45 female jack down to the RJ12 standard. 

Here's an example of an RJ45 jack that was incorporated into an an RJ12 faceplate.  When I bought the unit from my local building supply store, from the front, it looked like an RJ12.  From the back, it looked like an RJ12 because it had  6 spade terminals.  It was only when I plugged in my throttle and it wouldn't unplug that I discovered otherwise.  I snapped the jacks from the faceplate and discovered I had an RJ45 jack masquerading in an RJ12 faceplate.  (Fortunately, no damage was done to my command station.) 
In the photo above, the jack on the left has the typical RJ45 notch.  The jack in the middle is its RJ45 twin with 6 spade terminals.  The jack on the right shows the end results of ACCing a short piece of 0.040"x 0.250" styrene on each side of the jack to narrow the width down to the RJ12 standard (0.463"- 0.040"- 0.40"= 0.383" which is within the range for the RJ12 width). 

Some Things to Remember Before You Start
  • The secret to a good LocoNet is a good crimper - only the best!  Stay away from those plastic ones.  A good crimper will cost you about $45 (All prices are $Cdn). 
  • LocoNet wiring is wiring in parallel.  The literature refers to it as "daisy-chaining". 
  • Always tin the wires before you tighten them under the screws. The back of an RJ12 female jack has 6 screws that keep the spade terminals from the jack in place.  When you insert a wire and tighten up the screws, the screws will "guillotine" the wires.  Tinning the wires with solder adds strength to the wire. 
  • When you've got your female jack installed on your module, secure the cable under a wire staple.  This takes the strain off the coloured wires that are exposed. 
  • You'll save yourself a lot of headaches if you can locate some RJ12 "double female" extension cords.  It's the same as a 15/25 foot telephone extension cord that has a male plug on one end and a female jack on the other end - except the double-female plug has two female plugs molded into the female end.  Check your electronics supply shop.  In Canada, they're available at Princess Auto - regularly $4.99 but they go on sale every couple of months for $1.99.  I pick up a ½ dozen at a time. 
  • Alternately, locate a supply of RJ12 "single-female to double-female" plugs.  These are similar to the female-female "gender benders" except that one side has two female jacks. 

This is the crimper we use.  It's all-metal which allows us to get a good squeeze on the plug when we crimp on the wire.  As an aid to make sure I've got the wires oriented properly, I've painted on two dots - a blue dot on the left side, and a white dot on the right side.  This makes sure that I'm crimping the white wire to Pin 1 and the blue wire to Pin 6.  If you're in doubt, compare your crimp to that short piece of stripped wire that came with your Digitrax command station kit. 
Before we start wiring some jacks, let's make some test leads.  When installing the LocoNet, we don't want to take shortcuts.  At every step of the way, we want to make sure that our wiring/ crimping/ soldering has been done properly.  It only takes a couple of minutes to check that crimp, solder, or wiring. Here's some simple test probes that will save you lots of headaches. 

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