Thursday, January 23, 2014

Field replaceable NMEA 2000 connectors

It's was the stereo installer dudes who caused the problem. There are now two new speakers installed on each side of the T-top's electronics box. Their enormous size driven by two amps now assures the owner that the USGS's seismographs will register every time they are used. Unfortunately the auto stereo dudes didn't realized the single NMEA 2000 cable they tie wrapped their big wiring bundle to couldn't take the strain and the connector's pins were pulled out.

No big deal for me, work is work. The wire pull is torturous, so I'm going to use a Molex field replaceable NMEA 2000 connector to rectify the issue, and you're going to learn how to do it.

The bag has four parts, and assembly is straight forward, if you know the tricks to make it work. What isn't so clear are the included instructions, in particular the line that reads, "secure conductors to the appropriate conductors as shown." Well it's not shown for starters, and the how is somewhat elusive. Another case of inscrutable "Height of Brevity" technical documentation.

Let's start with the basics, and I will translate. Put all of the parts you can't put on the wire after the connector is installed on first in the right order. This saves you some interesting language when you stare at the left over parts. It's also good they tell you the black knurled ring thingy must be rotated clockwise to install. I don't know if I could have figured this out all by myself. I think it's one of those righty tighty lefty loosey sort of things.

This is what you end up with. Since the wire is hanging down, if I let go, gravity will kick in and the parts will fall off. So you need something to thwart gravity's insistent pull. A wad of tape, a tie wrap, or in my case not shown a pair of long jawed hemostats clamped on the wire. I use these to extract pull wires out of small holes, and before you ask, no the ends aren't burnt.

Step one, strip the outer case of the cable,  and remove all of the blue plastic wrap stuff. You want to end up with about an inch and a half of wires exposed. Take the blue wire and clip it short leaving it about three quarters of an inch long.

Good, now strip the blue wire's sheath back no more that one quarter inch. Did I mention the small jewelers screw driver? No? Well you will need one so go get it. Attach the blue wire to the blue post. You don't want a lot of wire hanging out in space afterward.

Now pick a wire,  any wire, and hold it on the connector as I did in the picture. Cut the wire where the red arrow is pointing. Now gather the remaining wires together and cut them to this new length.
It gets a little tricky here so listen up. The reason we cut the wires is they are now about the right length when installed. Strip them back about three eights of an inch, and twist the ends tightly.

The bare shield wire must also be twisted tightly. Here is the part of the design I don't like. The blue post is exposed, and the shield wire is bare. I never want the twain to meet. I have two choices here. The first is to take a piece of tiny shrink wrap I don't have, and don't shrink it on the bare wire. 

The second option is to take a piece of electrical tape, and cut a piece about a fat quarter inch wide, by three quarters of an inch high. Take this and fold it in half around the bare wire, up a bit, and leave it for the time being. Now things are easy. Carefully insert each wire into the correctly colored hole and tighten. The one with no paint is the black wire, and the gray painted one is the shield. When you're done take the piece of magic black tape and slide it down to the bottom protecting the bare wire from contacting the blue post.

Now just screw the parts together. If they don't screw on, try twisting them in the other direction. One or the other will work even if you're caggy handed. The black knurled piece doesn't screw all the way down, at least by hand, and I'm not going to try to force it.

It's a wonky design for a connector. You end up with the bare wire able to make inappropriate contact with the blue post. I think the device net standard should be redesigned so the shield wire is the center pin soonest. This will make my life easier. We can call it "Device Net 3000." The cable manufacturers will love it.  Kate sent the hand model out for a manicure, but found him at the watering hole instead.


  1. Hi Bill!
    Can you advise what p/n Molex connector you are using? I need to pull some N2K through some tight areas. Is there any field replaceable version for Ray Stng???

  2. Great Work!
    What is the part number for that connector? brand ? name ?

  3. Pedro, sorry for the delay. It's a Molex part and here is the link to their page.