Hey all, I'm hoping someone can help me or direct me to a post which covers this issue, but I'm not finding it by searching (maybe my searches are too specific?)

I have 1996 F150 5.0 with about 250,000 km on it, and a few weeks ago when I turned the key to start it, nothing happened, no power at all, not even enough to move the gauges or light up the battery light.

I immediately assumed it was a dirty battery terminal, and popped the hood to check the connections, they were clean and tight and free of corrosion, so I checked the key again and the truck started fine, but the CEL (perma-on due to removed cats) was off and my stereo was reset to demo mode as if I had disconnected the battery. (I should mention that once it starts it seems to run as well as it always has, and has run for hours without issue)

At first I wrote this off as a one time occurence, but then about a week ago the same thing happened again, no power, turn the key off then on, power but everything is reset.

I began looking into potential causes and couldn't figure out anything other than that it's probably an electrical problem...obvious in retrospect.

Then yesterday I went to make a quick trip to the grocery store and it did the same thing over again, and upon returning to my truck after getting my groceries, it failed to start yet again.

So the problem is becoming more frequent, and I have yet to find the cause/solution. Please help!