When I decided to put a new dashboard in my 1974 Spitfire I figured that I would go ahead and replace the 3 fuse panel with a larger fuse block.
I bought a ten station fuse block from Summit Racing and wir from British Wiring. Jason at British Wiring is very helpful and honest. he will sell wire in one meter lengths so you don't have to buy a whole roll.
My original 3 fuse panel had 1 red/green wire, 1 brown wire and 4 white wires on what I call the 'hot' side.
On what I call the 'load' side there were 2 red wires,4 purple wires and 4 green wires.
I bought approximately 16 feet of red wire, 16 feet of brown wire, 12 feet of purple, 16 feet of white, 16 feet of green and 4 feet of white/pink.
I cut the wire into 4 foot lengths.
Using spade connectors, I connected 2 red wires, 4 white wires and 4 brown wires to the 'hot' side of my new fuse block.
Again using spade connectors I connected 2 red wires on the same fuse as the 'hot' red wires, 4 green wires on the same fuses as the 4 white wires, 3 purple wires and the white/pink on the brown wire fuses. I also put wire markers #1 thru #10 on theses wires.
I then mounted the new fuse panel on the firewall behind the battery at the top of the right side glove box.
I bundled the wires together (wrapped them) and fed them across the underside of the dashboard to the left side where the original fuse panel was.
I removed the original fuse panel (squeeze the clips to pop it out) and pushed it as far into the engine bay as possible. With the original fuse panel out of the way I fed my new wires thru the hole and into the engine bay.
I cut the 'hot' side wires off the original fuse panel, spliced them to the new wires of the same color (red, white and brown), soldered them and covered them with heat shrink tubing. I have a heat gun but a hair dryer would probably work.
The I cut the 2 red 'load' side wire (panel and driving lamps)and spliced (etc.) them to the new red wires.
I then cut the purple wires, checked them with an ohm meter to see where they went and followed suit. I had one extra so I put it with another on one of the new wires.
I then followed suit with the green wires.
The last wire - the white/pink I connected to my radio so I could play the radio with the ignition off (radio is hot all the time) I turn it on/off with it's switch.
After all the splicing I pushed all the wires back into the car under the dash and popped the original fuse panel back into it's slot.