There are many misperceptions about requirements for replacing wire. The FAA has made several of their resources available on line. AC43.13-1B Chapter 11 makes recommendations regarding wire inspection, substitution and replacement. Paragraph 11-97 specifically addresses wire replacement. 11-98 covers terminal replacement. Manufacturer certification for aircraft wiring is available on PDF upon request.
Last year I was called to a local airpark for a Piper Cherokee with alternator whine reported by ATC. A leaking diode prompted an alternator overhaul. The owner mentioned two recent starter replacements. As I'm generally inspecting the engine bay I notice the absence of a ground cable between the engine and airframe. Both the starter and alternator need a large ground path to the battery thru the airframe to function properly. Older model Cessna and Piper wiring diagrams show component grounds, but are vague on specific locations and wire size. If you don't have a dedicated ground cable equal size of the starter cable between the engine and airframe, you will have alternator and starter performance problems.
Engine mounts have large rubber isolators that make poor electrical conductors. Cable housings may complete the circuit, but performance will be diminished and may pose a fire hazard if your entire electrical system attemps to ground thru one or two small cable housings. We installed a heavy 4 AWG equivalent braid on the Piper between the engine and airframe side of the motor mount isolators. The owner reported an obvious increase in starting power.
AC43.13-1B Chapter 11, Section 15 is dedicated to grounding and bonding. Scroll down thru the gallery for cleaning and corrosion control.
A common industry practice is to clean grounding surfaces with a stainless bonding brush and treat with an alodine stick.
Cessna used a number of different sized two piece shields for firewall feed thru. Note the 172M IPC allows 3 different hole diameters to accommodate wire bundle sizes. NAS557 split grommets are also inside the hole.
Contact me if you damage this nylon grommet and I can send a replacement.
Aircraft Spruce sells shield kits and several types of firewall sealant. Gallery displays customer supplied photos.
Techflex TechLace nylon wax finished LT1-S3-FB-BK is my all purpose lacing tape. I've tried synthetic rubber and it just doesn't lock knots like synthetic wax. Size 3 isn't too bulky and doesn't cut into your hands like smaller tape. Fiberglass LT4-S3-FD-NT works best in high temperature areas, but care must be taken during tying because it breaks much easier than nylon.
PPH voltage regulator harness shields are grounded by attaching the 1/4" ring terminal to a voltage regulator mount bolt. The FAA AC 43.13-1B Chapter 11 recommends the shields be grounded on both ends. Most avionics shops will recommend terminating all shields at one end only. Single point shield ground is required by all audio panel manufacturers for shielded wires used in audio systems. These would be aural warning, headphone, music and entertainment wiring.
CONNECTING SHIELD TO POWER THRU ANY MEANS WILL RESULT IN IRREPABLE DAMAGE.
I use Ideal 45-162 to strip tefzel insulation from shielded conductors. The blade can be adjusted for depth to cut into the insulation without going thru. This prevents shield damage by the razor. Then just bend the conductor around to break the insulation. A piece of rubber or emery cloth helps to pull the insulation free. Any razor will work, just be careful not to damage the shield while rolling the blade around the insulation. Should you choose to ground the other end of my harness, read the shield pigtail link provided above. I fold the shield over the outer insulation as an extra measure of protection. Then solder a wire to a piece of exposed shield and protect the joint with heat shrink. Ground the other end of that wire with a quality ring terminal. TYCO solder sleeves require a heat gun capable of melting solder.
AC 43.13-1B Chapter 11
11-89. SHIELDED WIRE - Shielded wire or cable is typically connected to the aircraft ground at both ends of the wire, or at connectors in the cable.
11-98. TERMINALS AND TERMINAL BLOCKS - g. Shielding should be dead-ended with suitable insulated terminals.
11-106. ELECTROMAGNETIC INTERFERENCE (EMI) - Use of shielding with 85 percent coverage or greater is recommended. Coaxial, triaxial, twinaxial, or quadraxial cables should be used, wherever appropriate, with their shields connected to ground at a single point or multiple points, depending upon the purpose of the shielding.
Avidyne AMX 240 Installation Manual
2.4.1 Electrical Noise - Ground loop noise occurs when there are two or more ground paths for the same signal (i.e., airframe and ground return wire). Large cyclic loads such as strobes, inverters, etc., can inject noise signals onto the airframe that are detected by the audio system. The shields can be daisy-chained together, and then connected to the ground lugs mounted on the back plate shown in Appendix B.
AMX240 Connector, J1 (Sub-D 44-pin, male on tray) - All shields should be grounded as shown, at signal source only. Other end remains floating(refers to audio wire only).
Alternator manufacturers have FAQ pages to assist customers with charging and noise issues. They're worth a read. The following are know sources noise.
IDEAL 45-635 Custom Stripmaster Lite pictured below is a prefered wire stripper for aviation. Die type blades have precisely machined counterbores with an inner ridge for stripping the insulation. Lower cost knife type blades can contact and damage the conductor. 45-635 is for thick wall Type EE insulation. Note the small gap around the standard wall Type E M22759/16 wire in the die. This combination strips well and puts less pressure on the expensive blades compared with Type E stripper 45-2133. Custom Lite frames are smaller and require less hand pressure than full size Custom frames.
Pre-insulated(PIDG) and uninsulated terminals are best crimped with a ratcheting type crimper as recommended in AC 43.13-1B Chapter 11, Para. 178. The 3 chamber crimper below is TYCO 58433-3, an affordable field grade crimper for AMP PIDG splices and terminals. This crimper belongs in every A&P tool box and crimps terminals for 10- 22 awg wire. The "T" head dual chamber 59250 is a high cycle manufacturing grade crimper.
Post hardware can limit available real estate when multiple cable lugs are installed. The right post inside anchor nut is typical of original solenoids and considerably thicker than the outside nut used for attaching cable lugs. This hardware combination works well with a single heavy duty lug. Note available thread space on the left post with a thinner AN316-5 nut and lock washer MS35333-41. Sky-Tec informed me replacing the thicker anchor nut is acceptable, be careful not to allow the post to slip inside the solenoid case. I always recommend the installer contact tech support prior to changing factory hardware.
As of 08SEP17 Hartzell Engine Technologies, parent of Sky-Tec, informed me of an inherited problem within Sky-Tec master solenoids shortly after acquisition. The contactor alloy corrodes and will not carry a load. Voltmeter will indicate correct voltage across with no current output. All solenoid production was permanently ceased. By SEP of 2018 Lamar purchased the Sky-Tec solenoid PMA's and product. You will notice Sky-Tec master solenoids are now 4 post instead of the older 3 post. Read Service Bulletin 72-A.
Silicon boots can be tough to install sanitarily. Below is a battery solenoid using boots with 2-3 conductors per post. Running every wire for a single post thru the boot allows complete encapsulation of the post and terminals. MS25171 boots come in -1 thru -4 sizes. My cable sets include appropriate boots. Dow Corning DC4 is a good dielectric grease-like material that helps manipulate boots over cables, be sure to keep conductive surfaces of the lugs free of this compound.
The gallery below shows the correct way to connect new Lamar dual coil post solenoids in Cessna 172M. Lamar chose to connect both sides of the coil externally. Early factory solenoid coils were attached internally on one side and externally thru a single 10-32 thread post.