On 6/22/2012, Brooks Schneider wrote:
"Had a condenser fail. Pretty disappointing, as Jeff Schlemmer rebuilt the distributor and had only put about 100 miles on the car. Condensers seem to be a lot more of a headache than they were when I was a kid and all cars had them. I'd still rather carry a handful of those around than convert to electronic ignition. We'd have been towing that GT last night if he had one of those".

Condensers have always been a fickled bunch, sometimes bad right out of the box, or can fail within a few hours of running time from new. Two tricks here. Always carry a spare condenser in the traveling toolbox, and never trust a new one without testing it. Install a new one in the car and run it for a few hours (or a week or two). Then put that one in the tool kit for a proven good spare part, and install a different one in the distributor.

If you feel like installing a new condenser as part of a tune up for preventative maintenance, you can put the old good running condenser in the tool kit for emergency spare. It is my experience that a good condenser can usually run about 100,000 miles before it will ultimately crap out, so no need to be replacing them with periodic tune-ups. My Mallory dual points distributor has had two condensers fail in 219,000 miles (so even good brand name parts are not forever). People who don't put so many miles on the cars might never see a condenser failure (but carry a spare anyway).

Addendum November 2013:
Lucas distributors typically have the condenser inside the distributor connected to the contact points and grounded to the case (which is grounded to the engine block). My Mallory Dual Points distributor has the condenser mounted and grounded on the outside of the distributor body with the lead wire connected to the distributor side terminal. My John Deere garden tractor has the condenser mounted and grounded on the coil bracket with the lead wire connected to the coil terminal which holds the points wire. These are all the same electrical circuit. The condenser body needs to be grounded, and the lead wire can connect anywhere between the coil and points.

This leads me to a tech tip that can be good for field service, especially if your condenser fails and leaves your car dead on the side of the road. Most condensers will fail by burning or disconnecting the internal bits, leaving it open circuit. A condenser shorting internally to ground is very rare. If you have a spare condenser in your traveling took kit (which everyone should have), there is a quick fix. You can screw the condenser bracket to the coil mounting bracket, and connect the lead wire to the coil primary points wire connector. For MGA this is the white wire with black stripe going to the distributor. You can leave the original failed condenser in place, as it is open circuit and does nothing. As such, you do not have to fiddle inside the distributor on the side of the road.

Additionally, you could prepare your spare condenser with two alligator clips. This makes a good diagnostic tool as well as a quick emergency road repair. Clip the condenser body to the coil mounting bracket, and clip the lead wire to the coil terminal (distributor lead wire).