1994 Jeep Wrangler tail lights

Nope, you have a broken ground wire. To prove it to yourself, look closely at those tail lights and you'll see both filaments, the tail light AND the brake light are glowing. If you remove the right rear bulb, the front ones, and possibly the side marker lights, the left rear one won't work at all.

Given the type of vehicle, it likely has a trailer wiring harness. That's the place to start looking. If someone spliced in that harness with Scotch-Lok connectors, you can bet the wires are corroded apart. Those connectors are used all the time but must never be used outside because they don't seal out moisture.

You have tail lights, so you know there's voltage getting to the bulbs. A test light will show the same thing. If you want to prove to yourself there's a bad ground, use the test light with its ground lead clipped to a metal part of the body or frame, then touch the probe to the ground wire for the tail light bulb. You'll find the tail light gets brighter and the test light glows but not full brightness.

The flasher has a little heating element inside. It doesn't get hot enough to flash when there isn't enough current flow. That is caused by that bad ground or not all the lights are working. If you have one light in each corner of the vehicle, you need a flasher made to operate two bulbs. If there's two bulbs in each rear corner, you need a heavy duty flasher made for three bulbs.

As a side note, if you've installed LED bulbs, they don't draw enough current to make the flasher work. You have to either replace the flasher with an electronic one, or add resistors to each signal circuit.