More info on calibrating the VDO instruments on thread
here. Suggest you download the VDO instructions via link on this thread if you are interested. I believe you can add a momentary switch to the calibration wires to achieve various programming functions particularly adjusting the speed sensor to display correct speed (mph or kph) and according to tyres fitted to front of car.
Regarding the spare fuse position on early cars, most plain red wires are a permanent unfused battery feed excepting the main 50 amp fuse. You can see the bombtail (distribution point) on schematic where multiple feeds are taken from battery, all being red wires. The numbers in red on schematic connectors simply indicate pin number sequence, the first and last often being shown. All wires can be traced on the schematics if you have patience. Each wire end has its colour code followed by unique number. Just a matter of finding the matching one indicating the other end of cable, which could be at a bombtail.
If you could explain what you need an extra power feed for it would help. Does it need to be permanent or via ignition switch for example.
