ISO 25981:2020

Road vehicles - Connectors for the electrical connection of towing and towed vehicles - Connectors for electronically monitored charging systems with 12 V or 24 V nominal supply voltage

This document specifies dimensional characteristics, contact allocation, tests and requirements of 7-pole connectors for electrical connections of electronically monitored charging systems of towing and towed vehicles. The electronic monitoring system is designed to detect 12 V and 24 V nominal supply voltage and to limit the current to 50 A, and this is a connector without any braking capacity. This electrical connection is intended for use with separable truck-trailer combinations in order to connect an additional battery pack of the trailer with the generator of the truck using an electronically monitored charging system. Additional battery packs in trailers are basically used with tailgate lifts, electrical forklifts or other technical equipment with high current consumption. This document further specifies a park socket used to receive and store the plug when it is disconnected.

Véhicules routiers — Connecteurs pour liaisons électriques entre véhicules tracteurs et véhicules tractés — Raccords pour systèmes de charge contrôlés électroniquement à tension d'alimentation nominale de 12 V ou 24 V

General Information

• Status: Published
• Publication Date: 09-Jul-2020
• ICS: 43.040.10 - Electrical and electronic equipment
• Technical Committee: ISO/TC 22/SC 32 - Electrical and electronic components and general system aspects
• Drafting Committee: ISO/TC 22/SC 32/WG 9 - Electrical connections between towing and towed vehicles
• Current Stage: 9060 - Close of review
• Completion Date: 04-Mar-2031

Relations

• Revises: ISO 25981:2008 - Road vehicles - Connectors for the electrical connection of towing and towed vehicles - Connectors for electronically monitored charging systems with 12 V or 24 V nominal supply voltage
• Effective Date: 23-Jul-2016

Overview

ISO 25981:2020 - Road vehicles: Connectors for electronically monitored charging systems (12 V / 24 V) - defines the mechanical, electrical and testing requirements for 7‑pole connectors used between towing and towed vehicles. The standard covers dimensional characteristics, contact allocation, tests and requirements for an electronically monitored charging connection (designed to detect 12 V and 24 V nominal systems and to limit charging current to 50 A). It also specifies a park socket to receive and store the plug when disconnected. This connector is explicitly a charging-only interface (no braking function).

Key topics and technical requirements

• Connector type: 7‑pole plug and mating socket with a park socket; floating contacts aligned to a datum position on engagement.
• Voltage/current: Intended for 12 V and 24 V vehicle systems; electronic monitoring limits current to 50 A.
• Contact allocation: Seven contacts with defined functions (two plus charging pins, multiple minus/feedback/control pins for platform/tailgate signals). Contact designations must be permanently marked on socket cover and terminal faces.
• Terminals and cabling: Terminals accept specified nominal cable cross‑sectional areas for high‑current and control pins (document lists separate capacities for contacts 1–4 and 5–7); connecting cables should conform to the ISO 4141 series.
• Dimensional features: Plug, socket and park socket dimensions and locking lever spaces are specified; socket cover must close automatically when plug is removed.
• Mechanical & electrical tests: Includes mismating prevention (IEC 60512‑13‑5), connection/disconnection force limits, endurance (10 000 cycles), and mounting feature strength (minimum mounting torque specified). Mismating requirement: no pin contact up to a defined force threshold.
• Identification and colours: Minimum colouring requirement - socket cover and plug insert light grey.

Applications and practical value

• Designed for separable truck‑trailer combinations to connect an additional trailer battery pack to the towing vehicle’s generator. Typical uses:
  • Powering tailgate lifts, electric forklifts on trailers
  • Supplying other trailer equipment with high current demand
• Ensures safe charging, prevents damage from wrong system voltage, and supports standardized interchangeability and testing for fleets and manufacturers.

Who should use this standard

• Vehicle manufacturers (truck and trailer OEMs)
• Automotive electrical component designers and connector suppliers
• Fleet operators specifying safe trailer charging interfaces
• Test laboratories and certification bodies ensuring compliance

Related standards

• ISO 4091 (connectors - tests & requirements)
• ISO 4141 (multi‑core connecting cables)
• ISO 12098 (15‑pole connector)
• ISO 7638‑1 / ISO 7638‑2 (braking system connectors)
• IEC 60512‑13‑5 (mismating / mechanical operation tests)

Keywords: ISO 25981:2020, 7‑pole connector, electronically monitored charging system, towing and towed vehicles, trailer battery charging, 12 V, 24 V, park socket, connector tests.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 25981
Second edition
2020-07
Road vehicles — Connectors for the
electrical connection of towing and
towed vehicles — Connectors for
electronically monitored charging
systems with 12 V or 24 V nominal
supply voltage
Véhicules routiers — Connecteurs pour liaisons électriques entre
véhicules tracteurs et véhicules tractés — Raccords pour systèmes de
charge contrôlés électroniquement à tension d'alimentation nominale
de 12 V ou 24 V
Reference number
©
ISO 2020
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
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Published in Switzerland
ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Dimensional . 2
4.1 General . 2
4.2 Plug . 2
4.3 Socket . 2
4.4 Park socket . 2
5 Application of the connector . 6
5.1 General . 6
5.2 Contact allocation . 6
5.3 Contact designation . 7
5.4 Terminals . 7
5.5 Connecting cable . 7
5.6 Colouring of plug and socket . 7
6 Tests and specific requirements . 7
6.1 General . 7
6.2 Mismating . 7
6.2.1 Purpose . 7
6.2.2 Test procedure . 8
6.2.3 Requirement . 8
6.3 Connection and disconnection . 8
6.4 Endurance . 8
6.5 Mechanical strength of mounting features . 8
Annex A (normative) Minimum functionality of the monitoring device . 9
Bibliography .10
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
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expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee, ISO/TC 22 Road vehicles, Subcommittee SC 32,
Electrical and electronic components and general system aspects.
This second edition cancels and replaces the first edition (ISO 25981:2008), which has been technically
revised. It also incorporates the Technical Corrigendum ISO 25981:2008/Cor 1:2008.
The main changes compared to the previous edition are as follows:
— references to ISO 4009 removed;
— corrections to Figure 2 socket.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved

INTERNATIONAL STANDARD ISO 25981:2020(E)
Road vehicles — Connectors for the electrical connection of
towing and towed vehicles — Connectors for electronically
monitored charging systems with 12 V or 24 V nominal
supply voltage
1 Scope
This document specifies dimensional characteristics, contact allocation, tests and requirements of
7-pole connectors for electrical connections of electronically monitored charging systems of towing
and towed vehicles. The electronic monitoring system is designed to detect 12 V and 24 V nominal
supply voltage and to limit the current to 50 A, and this is a connector without any braking capacity.
This electrical connection is intended for use with separable truck-trailer combinations in order to
connect an additional battery pack of the trailer with the generator of the truck using an electronically
monitored charging system. Additional battery packs in trailers are basically used with tailgate lifts,
electrical forklifts or other technical equipment with high current consumption.
This document further specifies a park socket used to receive and store the plug when it is disconnected.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 4141 (all parts), Road vehicles — Multi-core connecting cables
ISO 4091, Road vehicles — Connectors for the electrical connection of towing and towed vehicles —
Definitions, tests and requirements
ISO 7638-1, Road vehicles — Connectors for the electrical connection of towing and towed vehicles —
Part 1: Connectors for braking systems and running gear of vehicles with 24 V nominal sup
...