1985 Ford Thunderbird ongoing mystery cut off of all electr

Battery fully charged, positive and neg wires 2.0 upgraded size and clean, new starter solonid, all wires clean. Car worked perfect came back from store shut it off and 2 hr later when I went to start it starter went click and entire electrical went dead.
Pulled both wires cleaned them reconnected, [put battery on charger topped it off 12.80 volts. Hooked it up driving lights on, wipers work, ac blower on hit horn. Entire system dead. Took plus wire off battery reattached and clicking sound started from module behind radiator overflow tank. NO POWER period to anything! Left it unconnected returned in a few hours hooked up and lights on again. Hit starter DIED again. Jumped car with my hot 850Amp truck battery ZERO lights or electrical power only the clicking of what sounds like relays behind overflow tank.