Aircraft Electrical Terminal Connectors
Terminal connectors come in a standard color code of red ( which can look pink), blue and yellow and are the most common found in homebuilt aircraft. Hole diameters in the lug also vary in size to match with most common hardware you are likely to connect to. The red variety will be the ones you grab the most often. Red can be used on wire gauge sizes ranging from 22-16 AWG. Blue accomadates wire sizes 16-14 AWG. Yellow terminals fit 12-10 AWG. Be sure to order an adequate amount of the red ones. The aviation variety of terminal connectors is colored yet transparent. Being of a see through design allows the assembler to inspect the stripped wire for proper position and crimp, in the completed connector.
At the back of the terminal you will see a sort of flage or cuff. When you strip the wire, you want enough exposed wire to make good contact inside the terminal. The insulation should be over the wire in the cuff area of the terminal. This provides electrical, moisture and corrosion protection for the completed crimped terminal. If the exposed wire extends into the cuff simply trim off a bit of the exposed wire. If there appears to not be enough exposed wire in the contact area, strip off a bit more insulation.
In areas where you will likely need to disconnect a single wire during inspections or for regular repairs, one of two types of connectors can be used. The types of connectors used in this application are knife splices and PIDG connectors. The knife splices and PIDG connectors are color coded the same as terminal connectors for the same gauges of wire. They also crimp like standard lug terminals. A knife splice differs by having a flat tab of metal with a small hook at the end. A PIDG connector differs by having a male and female portion attached to either end of the wire. A PIDG connector male end has a flat rectangular blade at the lug end. The female side has a flat end with rolled sides and a locking or security tang buit in.
To install a knife splice connector cut your wire in two where you would like the joint to seperate, leave enough spare wire behind the joint location to strip and install the connectors and leaving a bit of slack in the wire. The slack will allow for connection of the two connector halves later. Strip your wire ends and twist the exposed wire, install a knife splice on each end. Do not allow too much wire to be exposed through the connector onto the blade portion or you will not be able to join the two halves later. Now criss-cross the connectors and then straighten the joint until the hooks secure the connection. Seperate the joint and slide a piece of insulated tubing or heat shrink tubing past one of the connectors. Reconnect the joint and slide the tubing over the exposed blades. If using heat shrink tubing, heat the tubing with a blow dryer and shrink in place. If using insulated tubing or heat shrink it is recommended to install a small plastic wire tie over the joint to ensure the joint will remain secure.
A PIDG connector is installed in the same manner as a knife splice only to make the connection you must slide the male portion into the female portion until the connection is complete. Pull outward slightly to ensure positive locking. If you pull too hard it will seperate as intended but will require a fair amount of pull to accomplish this. Secure with tubing and wire tie as described above.
Butt connectors are used to make wire to wire connections or to splice a new length of wire into the circuit. Simply strip the wire ends , twist the exposed wire and crimp. Wah-la the wire and circuit are whole.
If you prefer, a butt joint can also be accomplished by soldering and if multiple joints need to be installed all in one area, solder joints will be less bulky. Installing solder joints is entirely your option. As you progress in your build you will come to recognize where a solder connection or connector is your best option. You will likely use both throughout the electrical system.
To make a solder joint- slide a proper length of heat shrink over one of the wires. Strip the wire ends and twist ends. Dip or place a small amount of flux on the exposed wires. Dip the tip of your hot solder pen into the flux. Flux cleans the metal to ensure rapid heating and good contact. Test the solder pen for readiness by touching the solder to the tip. If the solder readily melts- the pen is ready. With a small amount of solder on the tip tin both ends of the wires. Lay the wires parallel to each other and get a small glob of solder on the pen tip. Heat the connection site with the solder pen and solder until good joint fusion is made. A continuity check may be made at this time. Clean any excess flux residue from the joint site as this can cause future corrosion at the site. If all is good slide the heat shrink over the connection site and heat until secure. AC 43.13-1 states that silver solder is not recommended in aircraft wiring because it can quickly become brittle causing joint failure. With that being said there can be certain special application areas where you may want to use silver solder.
When you have more than one wire or bundle of wires that will require a connection point you will want to select a single connector with multiple contacts. There is a large selection of multi-wire connectors such as Molex, AMP, and MS type connectors. When selecting these connectors keep in mind where it will be used. Will it be in an area of high vibration requiring a very secure lock mechanism? Perhaps the connector will be in an area out in the weather where water, snow, moisture, and corrosion may be a factor.
It is a good idea to label your wires and the circuit they belong to as you make your connections. This will save you a lot of time later if you need to troubleshoot the circuit.
Don't forget to secure your wires with lacing cord or cable ties. Spiral wrap and convoluted tubing can give added protection to wires in high abrasion areas.
Figure out what type of connectors and supplies you will require and put them on your shopping list.
While you are making all these connections and laying wire it would be a good idea to make a schematic of the circuit for future reference. To learn a bit on making your schematics see Schematic Drawings.