I have a trumpet vine about 5 years old that has never shown a hint of blooming. It does not seem to adhere to a trellis, but grows along the ground until I attach it to the trellis. It gets sunlight for about one-half the day. I also have another trumpet vine that gets full sun, but it has the same problems.
As far as the trumpet vine goes, you could try a couple different things. The first thing to look at is fertilizing. Be sure that you are using a fertilizer that is high in phosphorus (the middle number when you are reading a fertilizer label, such as 0-20-0). Also, avoid a excessive nitrogen fertilizer, which is a high first number (15-3-3). This may mean that you have to watch out where your lawn fertilizer is being spread, since lawn fertilizer is high in nitrogen. Be sure to avoid your trumpet vine when you fertilize your lawn. Also, moderate stress on the plant may induce flowering, so only water as needed and do not overfertilize.
Another way of inducing flowering from your trumpet vine is to do something called root pruning:
1) Cut a circular slit in the ground that is centered around the stem of the plant. The circle should have a diameter of two feet for every one inch of trunk diameter. Use a sharp, pointed shovel to make a slit by plunging it into the ground as far as possible, then rock the handle back and forth slightly to create a V-shaped cut. Proceed around the plant until the circle is complete.
2) Sprinkle bone meal or superphosphate into the opening at a rate of 1 cup per inch of stem diameter.
3) Use a gentle stream of water to wash the powder downward.
4) Once the water has disappeared, use your foot to lightly push down on either side of the cut to close the opening.
5) Replace the mulch over the worked area and water thoroughly to settle the loosened soil.