When you removed the automatic gearbox wiring loom, you noticed that the loom split in to two directions, just behind the starter.
The cable that goes up just after the starter is the speedo sensor, and the other thicker part ends up right next to the fusebox.
The speed sensor fits right into the plug on the manual gearbox, so no modifications there.
The thick cable splits out into 4 connectors.
The top one is 2 fat wires. These 2 must be connected somehow. Eg. soldered. This is a safty mechanism to prevent the car to be started in anything but Park. Connecting these overrides that.
The next one from the top contains the neutral and reverse switch.
The black wire is ground
The green wire is reverse
The white wire is neutral
I like only to have the cables that is needed on my car, so i took the loom a part, so i only had the 3 wires from the connector in the engine bay, to the gearbox.
The black ground wire was spliced over at the gearbox, so both neutral and reverse had a black ground wire connected to it.
Then i connected the green wire to the reverse switch and the white wire to the neutral switch.
The two other connectors in the engine bay was covered with some plastic to prevent water getting in to them.
All that is left now is reconfiguring the speedo, so it shows the right speed.
How that is done im not getting in to here. Some other guys here made guides for that. Besides it depends on a few different of things: wheelsize, diff, mph/kph.