I leave them on the plants until mid to late fall, never seems to be a problem. It is very wet here now as well so we'll see how it goes with the dry legumes.

Greenmtngal, it sounds like you did everything right. Picking dry (and nearly dry) pods when rain is expected can minimize spoilage, and make the difference between a good harvest, and a mediocre one. Placing the pods under a fan to dry was also the right thing to do. If the pods were nearly dry when picked, I'm a little mystified as to the reason for the mold. Were the pods in a single layer?

"Can I finish drying them in the oven or my dehydrator?"

That depends on whether the beans will be for eating, or for saving seed. If for eating only, then drying in the dehydrator, or in the oven on its lowest setting, is OK.

Seed to be used for planting must be handled more carefully. The oven would be out of the question, unless it is warmed by a pilot light only. Unless you have a blower only mode on your dehydrator (mine doesn't), the lowest heat setting is probably 95-100 degrees F. Even that much heat can damage beans - over time. A short time in the dehydrator, to get them half dry & stop molding, might be OK. Be sure to disinfect your dehydrator after you are done, following the manufacturer's directions for your unit.

If you have a lot of beans left to harvest, I would suggest using a window screen propped up in front of the fan, or something which will allow air flow from the bottom. The tarp is probably too dense to allow air to pass through, and may be the problem. Also, if you have a portable dehumidifier, placing it in the room would speed drying.

I dry fresh-picked pods under a ceiling fan in my living room, on some used cafeteria trays. The trays I use have a textured surface, so air can pass beneath the pods.

As to the moldy pods... don't throw them out just yet, unless they are so moldy as to be a health risk. Dry them as quickly as possible to stop the mold. It may be only on the outside of the pod. When the pods are completely dry (after about a week) shell out the beans & inspect them. If the beans themselves are moldy or discolored, throw them out; if good, keep them. I would suggest, though, that those beans be used for eating, not seed saving.

We would always harvest our beans by pulling up the whole plant by the roots, knocking off the dirt, tying them into bundles, and hanging them from the rafters of the garage, pole barn or tool shed to dry. We never picked individual bean pods for drying.