83 delta

I have a 1983 delta 88 royal with a 307ci motor.I went to start it and encountered the following problem.I put in the ignition key,turned it and got my instument warning lights okay but when I turned the the ignition switch to crank the motor over I lost all electrical power.No instrument warning lights,no headlights,nothing.After a short time the dash warning lights came back on,headlights worked,radio etc powered back up until I again tried to crank the engine and again I lost all electrical power.The battery shows 12.36 volts on a meter and I did get the car to start and run once.Now it wont run again and I just keep having the intermitent power problem as previously descibed when trying to crank the motor.Until now car has always run very well. I would appreciate any ideas as to what my problem may be.

Welcome to AF!
How are the battery cables and connections to the battery? Are they clean and free of corrosion? How is the condition of the battery cables, especially where the battery connections are, ( is the condition of the outer insulating sheath free of cuts or damage, etc. )? I would start looking at the simplest/ least expensive item to look at/fix which would be to check for corrosion either on the battery terminals or on the cable itself near where the cable end is. Corrosion can find a way under the outer covering and affect the cable itself. Try cleaning the terminals on the battery and inspect the cable looking for anything out of the ordinary as corrosion can affect a vehicle's starting ability. The car could be getting just enough power for the lights and radio, but not enough to crank the engine over.