1. An inductive pickup sensor with enhanced immunity to cross-talk comprising:

(a) an inductive pickup coil for inductively receiving a spark signal from a selected spark plug wire while capacitively receiving a cross-talk signal from a cross-talk source;

(b) an isolation transformer having a primary winding and a secondary winding, said primary winding coupled to said inductive pickup coil wherein said spark signal is inductively coupled to said secondary winding and said cross-talk signal is capacitively coupled to said secondary winding;

(c) a detector coupled to said secondary winding for converting said spark signal into a trigger signal wherein the amplitude of said cross-talk signal at said detector is reduced to obtain a desired amount of cross-talk immunity by setting an appropriate distance between said primary winding and said secondary winding; and

(d) a pair of terminals for coupling said trigger signal to a test instrument.

2. An inductive pickup sensor with enhanced immunity to cross-talk according to claim 1 further comprising an electrostatic shield enclosing said isolation transformer and said detector to reduce the amplitude of said cross-talk signal at said detector.

3. An inductive pickup sensor with enhanced immunity to cross-talk comprising:

(a) an inductive pickup coil for inductively receiving a spark signal from a selected spark plug wire while capacitively receiving a cross-talk signal from a cross-talk source;

(b) an isolation transformer having a primary winding and a secondary winding, said primary winding coupled to said inductive pickup coil wherein said spark signal is inductively coupled to said secondary winding and said cross-talk signal is capacitively coupled to said secondary winding;

(c) a detector coupled to said secondary winding for converting said spark signal into a trigger signal;

(d) an electrostatic shield enclosing said isolation transformer and said detector wherein the amplitude of said cross-talk signal at said detector is reduced to obtain a desired amount of cross-talk immunity by setting an appropriate distance between said primary winding and said secondary winding and by using said electrostatic shield; and

(e) a pair of terminals for coupling said trigger signal to a test instrument.