When you say flip the switch, do you mean setting the cruise speed by hitting the decel or accel switch?

When you do this, you capture the voltage generated by the speed sensor circuit on capacitor C19. This one is the most likely to be bad. It's the .1uF electrolytic standing up in the far corner next to the rectangular .2uF cap.

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
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