What is a SOT Lead

Sound On Top Lead (SOT Lead) Quadlock to ISO

What is a SOT lead?

I have been asked the following question a few times when people are wanting to fit their hands free kit into their standard car stereo, so here is the answer:

Basically a SOT (Sound On Top) lead is an adapter lead, which allows you to convert your vehicle’s manufacturer wiring loom, into a universal adapter plug known as an ‘ISO’ (International Organization for Standardization) plug. This ISO plug is a standardized plug that aftermarket in car audio manufacturers use to make chancing products easier.

The SOT side of things is needed to convert your vehicle wiring harness into this ‘ISO’ plug, then back into another vehicle manufacturers plug to allow you to keep the standard stereo working in your vehicle with such devices as an aftermarket hands free kit.

ISO Lead / Harness

The image above shows the standardized ISO plug, which features all your speaker connections in one block (the red/brown block) and all your electrical connections in another block (black).

SOT Lead / Harness

The image above shows you a “Quadlock SOT” lead, which features the ISO (male and female) connections at the top of the picture and the “Quadlock” connections at the bottom. Most GM manufacturers are now using this type of block, which features a mini ISO block, along with additional connections above and along side the block, as stereo’s become more advanced.

  1. Hi, purchased parrot mki9200 for my 2009 merc sprinter, audio/radio 5 system what sot lead?

    Please help


  2. hi james
    Ive just bought a parrot mki9200 to fit into a 60 plate corsa with a cd30 head unit could you tell me which connector i will need ?? Many thanks

  3. Hi. Thanks for the clear explanation above. Any idea which sit lead I’ll need for a Renault megane 2010 estate version. The head unit is standard radiosat classic.

  4. Hi James,

    I have just purchased a Parrot MKi 9200 …have read several different references to the installation to this. It’s going to be fitted into our Ford Mondeo Mk3 2002, it has the steering column remote which changes volume and channel, the cd unit is a 6006e 6 cd changer.

    I understand that I need a fully populated SOT-74 lead for this, though there are more than one!!! …so which one do I go for and can you suggest a good supplier?

    Regards Norm’s

    1. Hi Norman,

      Yes there are lots of makes and models of this cable, and there is also different cables for the Mondeo MK3 depending what stereo you currently have fitted.

      There are two SOT-074 leads available on the market, one is a quadlock type lead, and another is two connectors. The best way is to remove the stereo and see which connector you require.

  5. Hi James,

    I’ve just fitted a Parrot CK3000 into my 2006 Ford Focus. The Parrot kit works great but my stalk control for the stereo has stopped working. I used an SOT-92 lead to fit the kit with and it looked like there were some wires tin the quadlock connector which weren’t picked up by the SOT-92 lead. Could this be why it’s not working or is there something else I’m missing?



    1. Hi Tristan

      As this isn’t a fully populated cable, they will not work automatically. You can actually remove the plugs from the standard quadlock and put them into the SOT lead to allow you to keep the functionality of your stalk controls.

  6. Hi James

    I am experiencing a specific problem having had a Parrot 3100 installed professionally on December 10th 2012 into my Renault Scenic Mk111 featuring a BOSE ICE system bypassing the Car’s existing Bluetooth system which has been disengaged I’m led to believe, whilst using an iPhone 4S using the latest ios v6.1.1 operating system
    There is an unacceptable level of interference on both dial up and call receiving for which the Auto Electricians have diagnosed as a “missing” SOT lead made for my car specifically, however manufacturers and Parrot themselves say no such lead is made, but one could be made (takes weeks though) and further it could be my iPhone’s operating system causing the issue anyway.
    Parrot have had no single complaint other than mine about the problem but in the meantime I have to wait patiently for somebody to resolve the problem.
    If you can cast any suggestions on the problem I would be grateful.

    1. Hi Mark,

      I cant say I have come across anything like this before – With your description of a different system in the car (Bose) I feel that you have one of the latest model Scenic’s? I would assume (without seeing the car in person) that this is an amplified system, where your stereo runs a signal to an amplifier somewhere in the car, then the amplifier then distributes the sound to the car speakers.

      Basically the Parrot “blue box” is a mini amplifier, sending out an amplified signal to your stereo…. If I have the description above correct, the system is basically trying to amplify and already amplified signal, causing interferance.

      I know there was some issues with the Parrot 3100 back in the day with iPhones, and I usually tried to sell the users an MKi9100 / MKi9200 (back when I worked in the industry). The great thing about the MKi series is that it allowes for direct wiring into an auxilery input into the back of the stereo (which would be a cheaper option for yourself) or if the autoelectritian could find the amplifier, wire the Parrot kit into the output lines to the speakers (front in the 3100 series), bypassing and cutting the amplifier out when you receive a call / make a call.

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