Can anyone tell me why the plugs on my 1999 California wont spark when out of the head?
They certainly should do, assuming you have them touching some part of the engine, I would try another pair.
Yup, you need the plug body to be earthed.
Just a warning – if electronic ignition is involved (ditto for any injection system) try to avoid ‘running’ the ignition without a spark plug(s) (or one of those test air gaps) connected as a load, the amplifier may be protected against the very large Voltage pulses that will result if the HT side is open-circuit, or it might not! Err on the ‘might not’ … 
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