Aero ‘lectrics

De colores.


“…And that is why I love the many loves of many colors.” (Spanish folk song)

Molex connectors also come in chassis mount (as opposed to pigtail mount) versions for mounting on bulkheads, ribs, etc.

Walk down the Experimental flight line at Oshkosh, and I would be willing to bet that you will see paint jobs in shades of rose, crimson, ruby, garnet, scarlet, and many of the other 1000+ shades of red. Greens? A thousand more. Not to mention blues, violets, oranges, and all of the tens of thousands of other shades of the spectrum.

But what’s inside the fuselage in the electrical system? The same old whites and blacks, with an occasional red thrown in for good measure.

So, let’s see what colors might do for us, and at the same time, investigate a series of connectors that will make your wiring job a whole lot easier.

Color coded connectors have many advantages, not the least of which is ease of identification, but color coding off-the-shelf electrical connectors is well-nigh impossible. However, one manufacturer has given us a series of very reliable connectors that can be colored dozens of different shades. One manufacturer of dye has given us those dozens of shades that are available for a couple of bucks in any supermarket. You are about to find out how to make connectors for your airplane that cost less than a tenth the cost of what you might think of as an “aircraft” connector.

Red and black Molex connectors, along with a package of scarlet Rit dye.

The venerable Molex connector has been with us for at least 40 years and is likely to be with us for a long time into the future. Let’s get real about the reliability of this series of connectors. You may not see the connection between your washing machine, your car, and your airplane, but if you think about it, the washing machine is a vibrating monster with a hot, wet environment for the connector to work in, and I daresay your washing machine has an order of magnitude more hours on it than your airplane does. The automotive environment, with its heat, dirt, and G-forces (ever hit a speed bump that you didn’t see?) put stress on these connectors, yet they are used (literally) by the millions every year. Wonder why they are so reliable and inexpensive when they are churned out in millions? Ask the quality control and purchasing staff at GM, Ford, and Maytag why they specify them.

The Molex plugs after red and a black cold dye baths.

RST Engineering alone has tens of thousands of them that have been happily flying along without one single failure since 1974. I can’t stress enough that these are rough, tough, highly reliable connectors. Not only are the connectors and pins themselves inexpensive, but the crimp tools and extraction tools are priced in dollars, not hundreds.

Just for comparison’s sake, I looked up the same functional connector in a popular aviation parts magazine. The comparison was a 12-pin connector for #20 wire: $12 for the connector shell, and $1 for each pin. The same functional connector from Molex is 45 cents for the shell and 17 cents for a pin. Assembled cost for the aircraft connector: $24. Assembled cost for the Molex connector: $2.50. Roughly 10:1. Aircraft crimp tool: $275. Molex crimp tool: $21.

A male Molex pin, a red/white striped wire ready for connection, and a well-worn Molex crimp tool.

So, rather than continue to extol the advantages of this little connector, let’s do a little work on how you might want to get acquainted with this little gem.

First, what do they look like? A sugar cube on steroids. Pins are about the diameter of the copper ground wire of #14 Romex. They come in shell sizes of 1, 2, 3, 4, 5, 6, 9, 12, and 15 pins (with some oddball 24 and 36 pins in some varieties).

Second, where do you get them? If you Google “Molex 03-06-1122,” you will see that our old friends Mouser and DigiKey sell them, along with quite a few “Surplus Sam’s” that have them for pretty good prices. Use the tin-plated pins as opposed to the gold plate, as this produces a gas-tight soft tin to soft tin connection.

Third, and the central theme of this column, how do you get them in colors since they seem to all look like they are made of that milky-white nylon. Very simply, you dye them yourself. There are two ways of doing this: hot solution and room temperature. One takes hours, the other takes day(s). Both produce equal results.

Take Rit dry package fabric dye of your chosen color(s). Mix one package in a gallon of warm water with a tablespoon of plain vinegar. This is enough dye solution for about 100 connectors. Note that any color from a pale pastel to deep dark black may be used.

Hot Solution: Put the solution into a Crock-Pot on low. In about 5 hours the temperature will be about 180F (80C), at which time you put the connectors into the hot dye bath using a vegetable petal steamer. Agitate to get all the air bubbles out of the connectors. Agitate every hour for 3 hours, at which time the connectors should be the desired color. Do not overheat, as the nylon will soften and round the sharp edges necessary for good pin security.

Cold Solution: Put the connectors directly into the dye solution and stir to remove the air bubbles. Stir occasionally during the process to continue to dislodge air bubbles. It will take from one to three days to achieve the desired color as a function of the room temperature. No limit on time in the dye bath.

Both Solutions: Rinse the connectors thoroughly in warm water and allow to dry. Shake them from time to time to get rid of the entrapped water. If you like, put them in a cloth bag in a clothes dryer on very low warm temperature with slow agitation.

The metal wire only is crimped into the front crimp area (top), then soldered (middle). The wire and insulation is then crimped into the back crimp area (bottom). Note that male and female pins can be used in either plugs or receptacles.

As to the pins, we have developed a technique here at RST to keep the famous “broken wire” syndrome from happening. It is true that a soldered wire will prefer to break at the place where the solder gives way to the unsoldered stranded wire. The idea is to solder the wire to the front crimp on the pin, and crimp both stranded wire and insulation into the back crimp. This is the best of all possible worlds.

To wind up, we’ve got another famous Weir two-fer, having nothing to do with electronics. Ever have trouble reading your wrench sizes in dim light or back in the belly of the airplane without a drop light? A Sharpie marker and a little steel wool will take care of that. Simply rub the Sharpie over the wrench size, let the marker ink dry, then use steel wool to rub off the excess ink on the surface of the tool. The colored ink will remain in the indentations, making it easy to read the tool size. Unfortunately, the camera doesn’t do justice to what these tools look like in dim light, but I think you can get the basic idea from the photos.

I code my metric tools with a black Sharpie and my imperial tools with a red Sharpie. The red shows up better in dim light.

Metric and imperial tools after excess Sharpie ink has been removed with steel wool.

Keep reading and…stay tuned.

Jim Weir is the chief avioniker at RST Engineering. He answers avionics questions in the Internet newsgroup His technical advisor, Cyndi Weir, got her Masters degree in English and Journalism and keeps Jim on the straight and narrow. Check out their web site at for previous articles and supplements.


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