Prius Fusebox with exposed jumpstart terminal, The vehicle wiring harnesses will be behind this fusebox (Automotive Wiring). (C) Lunawisp, CC BY-SA 3.0 , via Wikimedia Commons

When you spend any time more involved with vehicles than reading a Haynes manual at some point you will need to know what someone means by KL31 in regards to automotive wiring for 12 V vehicles.

‘KL’ is the abbreviation for ‘klemme’ which is the German term for connector/connection, or ‘Klemmenbezeichnungen’. Klemmenbezeichnungen means Terminal designations.

This is mostly encoded in the German standard DIN 72552 – “Standard for labelling the electric terminals in automotive wiring.”.

However, in short, the KL codes you are most likely to want to know about are:

• KL15 is ignition switch position #2 (on)
• KL30 is battery positive, there will be ’12 VDC’ on this at all times
• KL31 is battery negative, (unswitched)
• KL50 is ignition position #3 (start)
• KLR means ignition switch position #1 (Accessory) In this mode the radio/IVI, windows, etc will be powered on, but the traction motor will not be enabled (ICE or EV), there may be limited HVAC (Heating Ventilation and Air Conditioning) due to the HVAC compressor, and the heater not being powered.

Normally when talking about KL30 and KL31, it is the positive and negative poles of the 12V (or 24V) vehicle battery.

What about EVs?

On an Electric Vehicle (EV) regardless of if it is a Battery Electric Vehicle (BEV), a Plug-in Hybrid (PHEV), or a Mild Hybrid Electric Vehicle (MHEV), there will also be a traction battery of some kind. While in the case of MHEV this may be only a 48 VDC battery. Some Vehicle Manufacturers (OEMs) use Blue cables).

If the voltage in the cables exceeds about 50 VDC, the “High Voltage” cables will be orange. Most EVs and PHEVs are powered at about 400 VDC, however, some newer EVs are starting to use 1000 VDC for the traction battery, and the EV Motor.

Historically the three modes of the KLR positions correspond to the opening and closing of three relays on a vehicle, however, in all modern vehicles there will be more states, and chances are fewer relays as semiconductor switching components have taken over.