I'm thinking about buying a Cobra 75 WX ST and was wondering if I can run the external speaker on the unit to my aux plug on my radio and listen over the radio speakers. Thanks.

 

The speaker output of the radio and the input of the aux jack are both different impedances and voltages. While you could connect it and use the volume control on the radio to limit the speaker output voltage and (hopefully) not damage your Jeep radio's aux input circuit, that's both risky and subject to distortion (because of the impedance mismatch). Fortunately, the circuit to make them work is pretty easy and inexpensive to build. You can learn more here ...

Speaker signal to line level

 

I should add that you may want to build it with a variable resistor, adjust it for satisfactory performance, then measure the resistance dialed in and replace with a fixed resistor.

 

Thanks! My little handheld did well on the trail, I could use it up to a quarter mile, that's more than I expected with that little antenna that I paid $40 for.

 

If the handheld has a headset/earphone output, then you should be able to safely connect that with a simple 3.5 mil cable to the Jeep radio aux input. The voltages and impedances may not be an exact match, but at least it's not pumping out a lot of power expecting low impedance like a speaker jack would be.