As far as I know the only way to get to the inside of the "boot" is to gently pull it loose from either the door or the door frame. However it will be very difficult to put it back and will likely tear when being removed. The voltmeter will be a lot of help at the switch end and could be at the door end, if you get the upholstery panel off. As noted above, the windows are paired diagonally on the relay / fuses. Also the console switches often go bad from dirt and soft drink drips into them. They can be opened and cleaned, sprayed with contact cleaner and put back together with good results. A CD or printed manual will give you the wire colors for the hot line and the up and down wires.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150