Have you ever made this mistake?

Thread Starter


Joined Jul 20, 2012
You have to do cabling, so you just say pin 1 goes to pin 1, but you do not realize that that you are just getting everything backwards with standard pass through cables?


Joined Jan 27, 2019
Male and female 'D' type connectors, mounted on a chassis, look the same from the wiring side but the pin numbers go opposite ways. It is easy to get the wires backwards.
I always hated wiring D connectors. Though I greatly enjoyed the solder cup terminals and the lovely joints they would make, the pin numbers were nearly impossible to read and on the front, where they were mirrored and confusing.


Joined Apr 24, 2011
I had (past tense as I don't use them anymore) the serious impediment of being about 50/50 in wiring a PIC programming interface. Just 5 wires but I stumbles over data and clock over and over. Even knowing my tendency, just as in Hofstadter's Law I would swap them over and over... even on PCB's!

As far as wiring D subs go, I will make pictures of the pinouts, and mark pin 1 (usually printed right on the part!) and get them right most of the time.

panic mode

Joined Oct 10, 2011
Never with cables and pinouts.... that would be silly.

But had mistake that is still seared into my memory.

while installing some upgrades on system i designed i was trying to temporarily move Keyence Vision to a position where i could better see result (camera was under conveyor). Should be easy, just needed to remove two power wires (24V and 0V) and connect power from another location. Camer cables were long enough so did not need to be touched. Well... user manual explicitly stated to not do anything like that while it is powered but cmon... ;)

It turns out there were two PCBs inside the vision system. camera connectors were on the lower PCB and just above them (on the top PCB) there ware PCB screw terminals for power. Coincidently that same where the terminals are was not supported (sigh). Maybe the wave soldering of through hole PCB terminal left a smidge of tin slightly longer, could not really say, they all looked the same. And gap between that 24V terminal and bare contacts of camera connector was very small, less than thickness of a credit card, maybe 0.25mm. Needless to say, mere touch of the terminal caused top PCB to flex a bit and cause short. Production was supposed to start in few hours and i had only two screwdrivers, needle nose pliers, wire cutter and swiss army knife... (sigh)

so the best i could do is trace the problem to a tiny SMT fuse. with no soldering iron or magnifier, i managed to make a tiny bypass jumper and - it worked. I finished the rest of work (dressing cables, programming etc.)

Short while later client arrived and i explained situation. they wanted it repaired by manufacturer and brought in spare from nearby plant.

All right, i dump the program into new unit and everything is working fine. Later that week I sent the unit back to manufacturer with photo of the board indicating defective fuse and explained the case and that otherwise everything was good. it took them several weeks, repaired unit arrived back with a nice letter with sorry that board could not be repaired, entire board was completely fried and beyond salvaging so they had to replace the entire PCB. Don't remember the price tag but it was pricey. Well i could not say anything, it was me that caused the problem while rerouting cables. I know that $0.2 fuse would do the job and i could have done it but fair is fair.

So i opened up repaired unit, placed piece of plastic between the two boards and assembled it. Better safe than sorry.
I used Keyence on many other projects but that was the last time i selected CV751 for a vision application.


these pictures are found on internet. one below shows wires without labels...tsk-tsk...

Last edited:


Joined Apr 11, 2010
My mistake was in moving from a prototype system to the final assembly.

It was an RC servo controller. When I tested the final assembly, the servos didn’t move. Turns out that the controller was rotated 180° when it was mounted. This particular controller had 16 sets of headers on both side of the board for a total of 32. I was only using 11.

So when I cabled the servos, instead of positions 1 thru 11, I connected them to 17 thru 27! On the opposite side of the board… I visually connected them to the same side of the board which had been rotated.



Joined Jan 27, 2019
I have the crimp tool and insertion pins, a little cleaner and quicker than solder.
Also no need to populate what is not used.
I was going to mention that I switched to those. For cables, i used the shells that have an 8-pin modular connector where the cable gland would otherwise be.

Pin them up, and plug in a male to male cable to each end. Fast, easy, and for most applications there was no problem using the flat silver satin pre-made cables in a desired length, though later I would make up Ethernet UTP cables as needed.


Joined Mar 13, 2020
I have a crimper that crimps the connection shell and the insulation support. I always have to stop and look, and even though I've figured out that it's the wire side that has the color codes for crimp sizes. Even still, I crimp sometimes backwards. And that's usually easy to find and (barely) costly to fix. I may have inadvertently wired a connector backwards at some point in life but I don't recall making that mistake.