kermitt

Got my airtech intercooler today and need to wire up the fans but I have a wee problem cos someone has bodged the wiring and fitted a maual fan switch. There is a red/black wire which comes out the loom together with the blue wire to the alternator which I have connected to a new alternator loom.
I have connected the red/black wire from the loom to a black wire which goes all the way back somewhere underneath the fuse box but not entirely sure this is correct but assume it must be.
I have the original fan plug but the brown wire has been cut short and the red wire has been connected to another red wire that goes to the '+'ve battery. Don't know where the rest of the brown wire from the plug is. Help please?!