Electrical goes dark and shuts off when ignition is turned from ACC to ON, suggestions?

I recently removed my stock radio and hooked up an aftermarket Kenwood
radio unit. I thought everything was gravy because the car appeared to be
working normally (including the aftermarket radio) when I had the key turned
to the accessory position.
When I tried to start the engine, all of the electrical went dark immediately.
The electrical does not come back on unless I disconnect the terminal from
the battery and reconnect. The car continues to lose power and go dark
whenever I turn the key ignition to ON.
Starter does not engage, engine does not crank, no electrical power.
I'm having trouble finding posts of a similar problem, any help or suggestion
is highly appreciated!