If only the right side doesn't flash I suspect you'll find the bulbs in one corner are not full brightness due to a bad ground wire. That will reduce the amount of current flowing through the flasher and it needs the right amount to heat up the heat-sensitive switching element. By jumping some contacts you probably added in some left side bulbs that drew extra current and made the flasher operate.

If the rear lamps have the round brass bases, measure the voltage on the base of one of them. You must find 0 volts. If you find anything more than 0.1 or 0.2 volts, follow the ground wire to where it's broken.

Another clue is to remove the left rear bulbs. If the right side ground is bad, the right side bulbs will go out. With a bad ground wire, current can't find a complete path so it looks for a different way to get to ground, and that is through the tail light filaments in the same bulbs, over to the tail lights in the left side bulbs, then through that ground wire. With the left bulbs installed and the right signal turned on, you'll see the left bulbs glowing dimly if you look real close.