Strange Electrical Gremlin

So after trolling for a few years when something went wrong with my P5, I decided to register and post a question.
About 3 months ago, the aftermarket radio that was in the car when I bought started cutting out when I'd use the blinker or hit the brakes. Lasted 2 days or so and was intermittent. Chalked it up to Gremlins.
A week ago, it started happening again on a more consistent basis. But mostly when it was warmer outside.
2 days ago, it was constant and not from any particular thing I did. Accelerate in traffic, idle at stop light, brake, blinkers, you name it the radio cut out.
So, I used so good old fashioned Redneck engineering and hit the front of the radio. I was so irritated at this point. Apparently that was a bad idea...Car went nuts. Everything electrical flipped out, Battery light came on, CEL came on, engine started to stall (thankfully I was at a light). Turned radio off, everything went back to normal, except CEL. Checked codes when I got home, P0304.
Briefly drove it yesterday after clearing code and everything seemed ok.
Just wondering if it is the sensor or is there some short somewhere, possibly related to the old radio.
Any ideas would be much appreciated.
Thanks,

that honestly sounds like a bad main electrical ground(the main one on the car) or a bad alternator. check all your connections at the battery and at the alternator, then check all the ground points make sure everything is nice and tight as well as corrosion free, then take it and have the battery and alternator checked at your local parts store

My wonderful wife took it to get the battery tested this morning...it's bad. Hopefully new battery with cleaned terminals will clear this one up. Thanks.

yeah if they were corroded and the battery was bad i would replace the terminal ends as well. but bad batteries can cause any number of issues, i have seen a ton working at autozone.

Terminals looked in good shape. Swapped out battery and nothing for 2 days. Hopefully that will do it.
On another note, I never noticed before but there's no battery hold down in my car. Anyone know where I can get one?

you can buy a universal one at most parts stores or if you want factory style a junkyard or dealer would be best bet

So this started back up again this weekend. Can anyone direct me to a post or link that would show me all the ground locations? Looks like I'm going to have to check and clean all of these.

Start with the battery to chassis ground wire.

Haven't had the time to check that out, but will do it this weekend. Of course this kind of stuff always happens with the worst weather possible. From 70 degrees to 40 degrees in 2 days. Gotta love that Maryland weather. Thanks.

Yep. [nods head]