How can I test the capacitors to see if they are good? What is the purpose of these things? Where can I get replacements?

 

Easy way is with an old VOM (volt - ohm meter). An old one with a meter, not a readout works great. Put the VOM on one of the resistance scales. Test the VOM by shorting the 2 leads together (meter should then read zero - dead short). Then put the meter across the 2 capacitor leads. A good capacitor will act like a short for a moment (needle will swing towards zero), and then go back "open". You may try it on a Digital readout version, but it will depend on the readout's response time.

A capacitor is 2 plates separated by a dielectric (insulator). These plates can be "charged" by connecting to DC voltage (which is what you have done above with the VOM on a resistance scale). Once charged, it can act as a battery (with a very short life, but note that super caps are replacing batteries in some application). A capacitor has the ability to "block" DC (direct current), but will pass AC (alternating current). They act as good filters for DC by shunting unwanted AC "noise" in vehicle systems, which is their prime purpose in most old automotive applications (short the noise to ground so that it does not affect the radio reception).

A capacitor is also used across the ignition points (however, it was normally called a condenser back then). It's purpose is to absorb the inductive spike from the coil that occurs across the points when they open. This allows the points to last much longer, and provides a "sharper" cutoff for the coil (therefore a higher output out of the coil). If you have ever tried to run a vehicle with a bad ignition condenser, you would know what I mean (spits and sputters all over the place - if it will even start).

As for sources, can't help, but bet most of the Vette suppliers should have replacements.

Plasticman

 

but.....

most capacitors fail when they no longer can handle their designed operating (working) voltage. When this happens they can open circuit and not properly filter or worse yet break down to a near short circuit when voltage is applied . The only true test of a capacitors effectiveness is with a good capacitance meter or analyzer. Unfortunately these are rather expensive. Cheaper models use a small applied voltage to determine capacitive value only.

The challenge with the VOM method of test is the same as with a cheaper Capacitance meter in that the initial applied voltage (mV) is very small and not generally near the capactiors designed working voltage (12+ V) or breakdown voltage of the capacitor, thus the capacitor may exhibit the signs of working at this low applied voltage yet fail when put into service.

If you are looking for suppression capacitors I would suggest that you contact Jack Humphrey at JackHumphreyH@comcast.net. Jack finds old Corvette capacitors and properly tests them. He can generally supply all the suppression capacitors found on C1 & C2 Corvettes.

 

Thank you for your detailed answers.