No  power from charged battery to dashboard or lights. Does not start.

Burnt-out fusible-link on battery +ve cable?

I'd check whatever is inside the underwood fuse panel.  Could be a funky battery cable. 

Edited March 17, 20188 yr by john in KY

NVM, misunderstood.

Edited March 18, 20188 yr by Bushwick

If you aren't getting anything at all it is probably the pos. side cable.

Does the horn or radio still work?

The exact same thing happened on my xt today ant I was thinking wtf? It's impossible to leave anything on to drain the battery completely with this car. Unlike my chevy van, and 86 GL,  which both can have the key removed at any position. Very convienent