'79 Super Turtle,

A condenser is another term for a capacitor. Capacitors are made up of many layers of conducting material separated by insulating material, with every other layer of conducting material shorted electrically. One set of these layers is one polarity and the other set is the opposite. This arrangement allows you to store more electrons in the negative set of conductors than would be feasible at a given voltage if the same surface area or volume was spread out in the open. The term "condenser" comes from the ability of this geometry to store electrical charges in a smaller volume.

Condensors or capacitors do not conduct direct current, but they do conduct alternating current. In the application noted the intent is to take the alternating current component, due to the interruptions in current flow resulting from the brushes and the commutator, and run it to ground while preserving the DC output to go to the battery. If the insulation system fails in the condenser you would know it because the system would not charge your battery correctly either and it would likely burn out the little black box, taking out of the electrical circuit. If the condenser is disconnected by this or another means you will detect a buzzing noise on the radio that runs with the engine speed - higher engine speed gives a higher frequency buzzing.

Hope this helps, Jim

(edit for clarity)

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)