Good point. I keep a squirt bottle of H2O
on my ignition bench to check secondary insulation. I little mist sprayed on the wires will make bad ones go nuts on the scope. A word of caution about low-tech spark testing...the later "E"-Core coils(small ones)should not be given an "impossible arc" to jump. The spark will find ground inside the coil core and cause an eventual failure.
I never saw many coil failures until the 560s came out with the squat coils on them.
ASE Master Tech
Mercedes Tech 20 Years
68 SAAB 96 Ice Racer
69 300SEL 6.3
70 300SEL 3.5