An Autocom official wrote this comment concerning Isolation cables. I quote,
"The main reason someone blows their accessories (or Autocom) is normally because they fail to understand the importance of using ISOLATION leads when BOTH the Autocom and the accessory are bike powered.
If your accessory runs on its own batteries, and you also use separate batteries in your Autocom, you can connect your accessory to your Autocom using a standard hard wired lead, because each device has its own independent isolated power supply.
If either device is run on internal batteries, and the other device is bike powered, you can still use a standard hard wired interface lead, because each device still has its own (independent and so isolated from each other) power supplies.
If BOTH your accessory and Autocom are bike powered, it means that they now share a common earth point (the bikes battery) and so now you have to be very careful not to use standard hard wired interface leads between your accessory and Autocom, because you will cause what’s called EARTH LOOPS (or ground loops)
Many audio devices use amplifiers that have what’s called common earth, in other words the amplifier/speaker earth is common to the power supply earth. Common earths are also particularly usual for audio inputs, to help reduce undesirable electrical interference noise. ALL Autocom Aux inputs use common earth (relative to the power supply) so that any noise picked up on the accessory leads is sunk to the power supply earth and so reduced/eliminated.
THE PROBLEM IS, that many accessories use what’s called INDEPENDENT EARTHS on their audio outputs, and while these don’t mind being connected to your Autocom if either of both devices are used with their own independent batteries, they are a problem if both devices are bike powered and you do not use isolation interface leads.
If both devices are connected to the bikes power you then create a COMMON power earth. If you now use an ordinary interface leads between the accessory and Autocom you cause the accessories audio output to become connected to its own power earth (via the standard interface lead, through the Autocom, down the Autocom power lead, to the bikes battery, back through the accessories power lead and BANG! You over heat the accessories audio amplifier until it BLOWS!
To stop this happening you HAVE to use ISOLATION leads when both your accessory and Autocom are bike powered."
