MIL-DTL-38999 connectors with their cavities, M22759 wire and shielded M27500, EMI backshells, boots and sleeving as real components; 1:1 layout, bill of materials with manufacturer and part number, PDF drawings with title block, and one revision for every approved change. All in the browser, with data on servers in the European Union.
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A military harness has to work at −55 °C and at +125 °C, soaked in salt fog, after hours of vibration and shock, next to radios and equipment that radiate and must not be disturbed. And every one of its components has to prove where it came from and which revision of the drawing it meets.
MIL-STD-810 testing puts equipment through temperature cycling, humidity, salt fog, sand, random vibration and shock. Wiring answers with ETFE or PTFE wire, sealed connectors with anti-vibration coupling, adhesive-lined boots and respected bend radii. A street-grade harness does not reach the second test.
MIL-STD-461 limits what the system emits and what it must withstand. In the harness that means shields terminated over 360 degrees in EMI backshells, twisted pairs for the buses, separation between signal categories, defined grounds and shield continuity end to end. A badly terminated shield is an antenna.
Every part number with its manufacturer and CAGE code, every lot recorded, every conductor marked and every change approved as a new revision. Acceptance documentation has to match the delivered harness, and the obsolescence of a connector can force a revision years later.
Materials, connectors, electromagnetic protection, identification and configuration control: what sets a military harness apart from an industrial one, written for the people who will design, document or build it.
The wire in a military harness almost always belongs to the M22759 family: copper conductor with thin-wall fluoropolymer insulation. The slash number tells you the variant: sheets /32 and /34 are cross-linked ETFE with tin-plated copper for 150 °C; /33, /35 and /41 to /46 use silver- or nickel-plated copper and reach 200 °C; sheets /11 and /12 are PTFE with silver, the classic high-temperature reference. The conductor plating is not a detail: it sets the service temperature, corrosion resistance and the crimping procedure.
Sensitive signals and data buses (MIL-STD-1553, CAN, RS-422, Ethernet) run in M27500: a multi-conductor with two, three or four M22759 conductors inside, one or two braided shields (tin-, silver- or nickel-plated copper) and an ETFE or PTFE jacket. The part number encodes gauge, conductor count, inner conductor type, shield material and jacket, so two "22 gauge" M27500 can be different cables. The bill of materials must carry the full part number.
Gauge is chosen for current, voltage drop and, in airborne installations, from the AS50881 table, which sets the minimum mechanically acceptable size in each zone (a conductor that is too thin breaks under vibration before it overheats). High-strength copper alloy is reserved for gauges 24 and 26, where pure copper does not survive fatigue.
M22759/32-20-9) and the colour.MIL-DTL-38999 is the circular connector specification for defence and aerospace. It has four series: Series I (bayonet, lightweight, the basis of motorsport connectors), Series II (low-profile bayonet), Series III (triple-start thread with anti-vibration, environmental sealing, the most widespread in current programmes) and Series IV (quick cam coupling). In Series III the receptacles are D38999/20 (flange), /24 (jam nut) and /25 (in-line), and the plugs are D38999/26.
After the sheet number the part number carries the class (shell material and finish) and the shell size, the insert arrangement, the contact type (P pin or S socket) and the keying (N, A, B, C, D, E). Common finishes are W olive drab cadmium over aluminium (conductive, 500 h salt fog), F electroless nickel (conductive, high temperature), Z zinc-nickel (the cadmium-free alternative increasingly required under REACH) and stainless steel or composite shells for specific environments. The choice affects shield conductivity and galvanic compatibility with the backshell.
Contacts are M39029, crimped with an M22520 tool and a positioner for the size (22D, 20, 16, 12, 8, plus coaxial and fibre). Every insert arrangement has its mix of sizes; a 22D cavity only accepts its own contact and wire. A connector with unused cavities gets sealing plugs of the corresponding size, it is never left open.
| Series | Coupling | Sealing | Typical sheets | Usual application |
|---|---|---|---|---|
| Series I | Bayonet | Environmental | D38999/1 to /8 | Light equipment, basis of Deutsch AS and Souriau 8STA |
| Series II | Low-profile bayonet | Limited | D38999/9 to /19 | Inside equipment, tight space |
| Series III | Triple-start anti-vibration thread | Environmental, EMI | D38999/20, /24, /25, /26 | Current land, naval and airborne platforms |
| Series IV | Quick cam coupling | Environmental | D38999/40 to /47 | Blind mating and fast maintenance |
The backshell (AS85049 family) is the rear accessory of the connector: it holds the harness, relieves strain and, in its EMI version, terminates the cable shields to the shell. The correct termination is 360 degrees: the shields are opened and clamped under a band (Band-It or similar) or a termination ring against the backshell cone, so that shield current reaches the shell around the whole circumference and not through a pigtail. A two-centimetre pigtail cancels the shield's effectiveness above a few tens of megahertz.
MIL-STD-461 defines the emission and susceptibility tests (conducted and radiated) the system has to pass. For the harness that translates into concrete rules: a continuous shield from end to end, terminated at both connectors unless the grounding scheme says otherwise; buses in shielded twisted pairs; separation between signal categories (power, digital, low-level analogue, radio frequency) with minimum distances or overall shields; and a documented grounding topology, with the reference point of every analogue signal defined on the drawing.
Where the threat level requires it (lightning, HIRF, electromagnetic pulse) the harness carries an overall braided shield over the bundle, also terminated over 360 degrees, in addition to the individual shields. The overall shield is specified by optical coverage and material, and its termination is part of the harness drawing, not a workshop detail.
The harness is protected according to the zone where it is installed. The usual options are braided sleeving of expanded PTFE or Nomex, light and abrasion resistant; fluoropolymer or elastomer heat-shrink (Raychem DR-25 and its qualified equivalents) where sealing and fluid resistance are needed; PTFE or PEEK convoluted conduit with a ground conductor where there is a crushing risk; and resin potting at connector exits that will never be repaired. Each zone of the vehicle or equipment defines its combination.
Adhesive-lined moulded boots seal the backshell exit and add strain relief; moulded transitions do the same at every breakout. Minimum bend radii come from the wire and the conduit (as a rule, ten times the bundle diameter in fixed runs, six in moving runs) and must be respected in the layout, not discovered at installation. Separation from hydraulic, oxygen or fuel lines and from other wiring categories also comes from installation practices (AS50881 in aerospace, the programme specification on land and at sea).
Lengths are taken on the platform or on a 1:1 formboard derived from it, with service loops at every connector to allow two or three re-terminations. A military harness is built on that board and checked against it before it ships.
Every conductor and connector is marked according to the drawing: printed heat-shrink sleeves or UV laser marking on the wire, with the wire identifier at regular intervals, and a harness label with part number, revision, serial number and manufacturer. MIL-STD-130 governs the identification of delivered items (and UID marking when the programme requires it); conductor marking follows the programme's wiring practices.
Traceability requires the bill of materials to identify every component by its standard part number and manufacturer (with its CAGE code), wire and contact lots to be recorded per harness built, and any manufacturer substitution to go through approval. Obsolescence is routine in twenty-year programmes: an insert that goes out of production forces a drawing revision and a form, fit and function analysis of the replacement.
Configuration control is what turns all of the above into something auditable: every change (a new signal, a corrected length, a substituted connector) produces an identified revision, with its reason, date and approval, and the delivered harness has to match exactly the revision on its label and in the acceptance documentation. Working "on the usual file" without revisions is the fastest way to build a harness that does not match its drawing.
Before the protection is closed, continuity is tested pin to pin against the connection table, insulation between conductors and to ground (typically 500 V DC or per specification), and shield continuity and the termination to the backshell, with defined maximum resistances. Then come crimp inspection (pull force by sampling, visual inspection per the tool manual), dimensional control of lengths on the formboard and, where the programme requires it, environmental tests on qualification units.
The documentation that travels with the harness usually includes the manufacturing drawing with the layout to scale, the connection table (from which connector and cavity to which, with gauge, colour, marking and length), the bill of materials with manufacturers, the lot record and the test results, all referring to the same revision. Aerospace programmes add the first article inspection report (AS9102). If the drawing and the table come from the same source as the harness, consistency between them stops being a problem.
| Standard | What it covers | What it demands from the harness |
|---|---|---|
| MIL-DTL-38999 | Circular connectors | Series, class, finish, insert and keying specified |
| AS85049 | Backshells and accessories | 360° shield termination, compatible finish |
| M22759 / M27500 | Wire and shielded multi-conductor | Full sheet number, gauge, conductor plating, shield |
| AS50881 | Wiring practices | Minimum gauge, separation, radii, marking, installation |
| MIL-STD-461 | EMC: emissions and susceptibility | Continuous, terminated shields, twisted pairs, grounds |
| MIL-STD-810 | Environmental testing | Materials and sealing for temperature, vibration, salt fog |
| MIL-STD-130 | Item identification | Harness label with part, revision, serial and manufacturer |
Each row is a need from the guide and the concrete feature that covers it. harnessPRO does not simulate or certify: it documents the harness so that the drawing, the connection table and the bill of materials always come from the same source.
Place the units with their 38999 connectors and join the cavities. Mark the buses as twisted pairs, define the ground splices and note the category of every signal to respect separation in the layout.
Load the drawing of the installation zone, place the connectors where they go and trace the harness with a branch point at every breakout. Orient the boots and check lengths, service loops and radii.
Bring in the D38999 with their cavities, assign the specific M22759 and M27500, add contacts, plugs, backshells, bands, boots and sleeving by the metre. Export the BOM with manufacturer for the approved source list.
Generate the PDF with the 1:1 layout, the connection table and the title block with part number and revision. Save the revision with its reason. When the change comes, open a new one and compare.
The reference family is MIL-DTL-38999, above all Series III (D38999/20 receptacles and D38999/26 plugs): triple-start threaded coupling with anti-vibration, aluminium or stainless steel shells, environmental sealing and M39029 contacts. Series I is used for panels and light equipment; Series IV for high density. The finish (electroless nickel, zinc-nickel, olive drab cadmium) depends on the environment and the programme's material restrictions.
Wire from the M22759 family with ETFE or PTFE insulation: thin wall, resistant to fluids and abrasion, from 150 °C with tin-plated copper to 200 °C with silver- or nickel-plated copper. Sensitive signals and data buses run in M27500, a shielded multi-conductor built from the same conductors. These are the wires that AS50881 wiring practices take for granted.
It is the rear accessory of the connector (AS85049 family) that leads the harness out, provides strain relief and, in its EMI version, terminates the cable shields to the shell over 360 degrees. Without that termination the shield becomes an antenna and the harness fails the MIL-STD-461 electromagnetic compatibility tests.
The usual ones are AS50881 (wiring selection and installation practices), MIL-DTL-38999 and AS85049 (connectors and accessories), M22759 and M27500 (wire), MIL-STD-461 (electromagnetic emissions and susceptibility), MIL-STD-810 (environmental tests) and MIL-STD-130 (item marking and identification). Each programme adds its own wiring specification.
With a bill of materials that identifies every component by its standard part number and manufacturer (with its CAGE code), wire and contact lots recorded per harness, every conductor and connector marked according to the drawing, and configuration control in which every change produces an approved, traceable revision. The drawing and the connection table must match the delivered revision exactly.
Yes. You define MIL-DTL-38999 connectors with their cavities from the catalogue or the library, M22759 and M27500 cables as parts, twisted pairs for the buses, backshells and boots as accessories; you lay out the harness at 1:1 with real lengths; and you export the BOM with manufacturer and part number and the PDF drawings with title block and connection table. Every change is kept as a revision with a snapshot.
No. harnessPRO stores harnesses on its own servers in the European Union, uses no third-party services to store designs, and lets you export and import the whole project as JSON so you can also work in isolated environments. For programmes with classification requirements, see the terms of service.
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