You are right there if your speedo is the one in the picture. It is confusing because usually only speedos with reverse come with four wires colour coded as yours. Speedos without reverse come with only three wires (red, blue, black). Well, everything should be fine then but if your soldering skills are good you should redo that mess at the red/yellow wires. Leave the capacitor there (solder it to the red), it can't hurt.
Team Greasy Weasel
The best upgrade to any car is some driver skill.