I have added an additional fuse box under the dash on the passenger side this uses the same type of fuses as main fuse box. This is used to provide power to the Radio, Aux Socket and screen washer motor as can be seen in photo below. These items are fed with red wires so its clear they are additional to original wiring
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The brown feed wire is connected to one side of the fuses and is fed from the original fuse box. Seen in photo below with yellow connector just showing. This is the power fed side to the permanent live fuse, if you connect to the lilac as suggested by BMC you new power will also be protected by the original fuse. The choice is yours.
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