Electrical issue with zero responceof battey

I have a 1996 XJ6 VDP. One day (about a month ago) after a rain storm, I went to my car to get into the trunk. I pushed the trunk button and nothing. Zero acknowledgement of any kind of power. OK, so I opened the drivers door, and pushed the trunk "tab" next to the left side of the steering column. Again "zero" acknowledgement of any kind of electrical power, Hummm. OK, then I decided to get the key, and start the car. As I put the key in the ignition and turned it, (again) nothing!

No dash instruments, no lights on, Nada, nothing. I'd just been driving the car two days before and all was good. With a key I was able to get into the trunk, and the battery is fine. Reading another post on this site, I've suspect that it could be a relay that's failed. I've ordered a (digital) work shop manual in order to figure this out.

A few days before (and one or two times in the past) when I started the car, it had a "transmission" light come on, on the left side of the instrument panel, and the car would going what seemed like a "safe mode".

Simply turning the ignition off, waiting a bit and re-keying the ignition and this "safe mode" and trans idiot light would have gone away, and all was fine. This happened about 3 times in 6-8 months.

When I original got the car (8K ago) it was having idling issues that seemed to have been solved by running Marvel mystery oil in the fuel. After about 6 tanks of gas all idling issues were gone, AND was getting 27 MPG on the highway.

At the moment (and until I get a manual for it) it's like a stone, There is no (absolutely zero) acknowledgement of electricity through the car, so it has to be a primary circuit, and when I read the posting (and answer to it) about the possibility of it being a relay, I've decided that when the manual comes, that's going to be my starting point.

ANY and all help would be greatly appreciated.

Thanks

Stan L.