Shown below is the output from a Spectrum 128+2 as displayed on a Japanese Sharp CZ-614D monitor. The pins required on the Spectrum side are:
Red, Green and Blue connect directly to the monitor, and a Ground connection is also necessary. The monitor cannot deal with the composite sync directly however, so an LM1881N was used.
The composite sync is connected to pin 2 of the LM1881, with the composite sync output from pin 1 then fed to the monitor's horizontal sync input (pin 14). Vertical sync is output on pin 3 of the LM1881, and this is similarly fed to the monitor's vertical sync input on pin 15. The LM1881 requires a power input of between 5V and 12V on pin 8 and it must also be grounded.