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
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
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
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).
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
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.