This letter comes from a very frustrated Probe owner who recently installed a new car stereo. Stereos can do weird stuff, as you can see by Jeff's story:

I recently bought a new radio for my Probe GT. I also bought the direct wiring harness. The wiring all went together fabulously, I can hear music at a very low level, but the problem is that at any kind of reasonable volume the speakers either cut out or just buzz. I had thought maybe it was the speakers, so i bought normal factory speakers and still the same result. So then i tried to run straight off the battery, red to red and black to a ground. I ran the yellow, or ignition , to the red as well. I think this may be my problem. Should I try to run the ignition wire to just bypass the car's wiring completely? Or do you have any ideas what i can do to use the already installed factory wires? Please help, While listening to the exhaust in my car was fun at first, I kind of get tired of listening to the same song over and over again. I just walk around singing it all day. Let me tell ya, no one is a fan of my humming. Thank you for your time- Jeff

Jeff, it sounds like you're radio is doing what we call "clipping." This means that the internal amplifier isn't getting enough electrical flow to handle high volumes. You were smart to test it on the battery. To fix it, you should try a couple of things. First, I would check the ground connection in the dash. You can do this by taking a volt meter and running the positive side to the battery (might need some extra wire to make the leap) and the negative side to the ground wire on your radio wiring. If you aren't sure, they are probably labeled on the wiring that came with the new radio. It should read 12 volts. If it doesn't, you have a faulty ground wire. You can install a new ground wire to anything metal that isn't isolated by a washer or other nonconductive material. Basically any easy to access screw. Check it with the volt meter to be sure. i would just attach a new ground wire to the car and then run it to the new radio. If it's not the ground connection, you probably have a weak positive connection. Again, check it with the volt meter. Check the 12V+ constant wire (usually red, but should be labeled 12V+ or something), then check the 12V switched wire with the ignition turned on. This is the wire that makes your radio turn off when you turn the car off. If all else fails, you can run new positive wires, but unless you've done some wiring, you should proceed with caution because a misplaced wire can cause a serious meltdown, or fire. Trust me, I've been there -- 3 amps running off a single positive cable. Hey, I was only 17!