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.
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).
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.