legacycentral bbs

I have been having this issue for a few weeks now. Upon searching I have found it is something that comes up often. I trouble shot what feels like everything that was mentioned, and I'm coming up empty handed.
I have checked the relay, it works fine. All fuses are working properly, none are blown. I got another illumination control unit, and the problem persists.
I bought a new battery because the voltage was low, so I figured it wouldn't hurt to go that route. Still nothing.
The charging system is working properly, the alternator is producing the correct voltage while idle. Mechanically there are no other signs anything else is wrong. I'm ripping my hair out here!
My last step is to check all my grounds, but that feels like a reach.

The car does have an aftermarket radio, so I pulled it out and checked all wiring, made sure nothing was grounding out. Everything looked fine, behind the stereo.

What am I missing?

This is also worth a mention. It made me go towards a grounding problem. I killed my battery while seeking this problem (left the door open). I grabbed the charger to charge the battery, and while it was charging, the marker lights and tail lights start working! Once I took the car off the charger, they didn't work again. I couldn't replicate that situation though.

You must have a burned up ground somewhere. Some key points are under the front seats/carpet. Under the dashboard on the driver's side of the radio. I think passenger side as well.

If you have a hard time finding the burned up ground, I bet a ground wire kit would get you by in the meantime.