Maybe this will help:

Trumpet Creeper Vines should be thinned throughout the growing season and cut back in winter to prevent aggressive spread.

Posted by bhrost zone 5 NY (My Page) on Sun, Oct 23, 05 at 9:55
Both trumpet creeper and wisteria are fairly rampant growers, and will require occasional pruning both to keep them within bounds and encourage flower production - if left largely unpruned, they will expend a lot of their energy on vegetative (leaves, shoots) growth and direct less of it toward flowering.
As a broad general rule, if you are going to prune vines, it is best to prune them in the period after they complete flowering. It is best to avoid pruning them in the period leading up to their next flowering, because you are likely to inadvertantly prune off many of the future flowering buds and so lose much of your next flowering display (the flower buds may not be readily apparent while you're pruning). How long this window of pruning opportunity lasts depends upon the vine and is something you will get a feel for with experience. Of course, if the vine is a total mess due to neglect, you may want to prune harshly regardless of the timing so as to get it in bounds and train it for the future.

Vines that flower most effectively in the spring, such as Wisteria, do so on the growth of the previous year. Thus, if you prune Wisteria too late in the previous summer and fall, you are likely to have a non-flowering wisteria in the spring because you've pruned away most of the potential flower buds. In my experience, the latter do not even become apparent until the springtime. You want then to do major pruning on wisteria in early to mid-summer. Long, wispy shoots can even be pruned away in the fall because they are unlikely to produce flowers next spring. It is substantial branches/branchlets that you want to avoid late pruning on. As you put your garden to bed for the winter, you ideally want your Wisteria to be a relatively compact woody entity with a lot of somewhat short, thick woody spurs (not stubs) coming out of a main trunk and at most a few major branches (assuming you're not trying to cover a tremendously large space with one vine that is)- you don't want a lot of small diameter but comparatively lengthy branches shooting out everywhere from the main trunk and limbs.

As with any vine, shrub or tree, when you prune you ideally want to prune back to a bud - you don't want to leave stubs protruding. Creating your framework of comparatively short spurs (the type of architecture most conducive to wisteria flowering) may take a couple or more seasons to develop, particularly if pruning has been misguided in the past and/or you need your Wisteria to grow and cover a large space - once it is as big as you want it to be, you can direct your pruning efforts toward developing the short spur framework. Wisteria will sometimes produce flowers after leafing out in summer on new growth (particularly if it didn't flower in the spring), but this is usually ornamentally ineffective - it is the spring flowering before leaf-out which gardeners aim to achieve and towards which proper pruning efforts should be directed. There have been many good articles written about Wisteria pruning over the years, and I encourage you to seek them out to learn the nuances. I've dealt mainly with generalities above.

Trumpet creeper flowers in summer on growth of the current year, so it follows that you can prune it freely in the autumn but should be wary of particularly late spring to early summer pruning lest you remove flower buds. It's my impression that pruning for Campsis is generally less tricky than for Wisteria, and you're likely to get flowering even if you make some mistakes, whereas improper pruning is the reason why some wisterias seem year after year to not flower at all.

Good luck with your efforts.