Loss of imput signal from Lube oil, Coolant Temp and voltage.

My Father in laws's Royale shuts down after 5 or so minutes. The indicator panel shows "Low Battery Voltage" when I press the gage button, I see the volts are at zero, the oil pressure is at o and cranking does not increase the pressure, plus the coolant temperature goes to 304.

As the car cools off, the voltage slowly returns and the temperature come down as expected with the corresponding voltage increase. I have tried blowing air on all the components and connectors to see if it has a cooling effect but no luck there.

Measured voltage at the battery, on the relay box, on the fuses in the relay box are normal.

I have replaced the coolant temp and lube oil sender. I have wiggled every wire and connector I can find, I have tried to trace to a common connection but no luck there.

The engine runs fine when running, the coils have spark when in the failed condition, fuel pressure is fine, FP regulator is fine, the cam position indicator and crank indicator was replaced last year.

I think it is a common connection or relay failutre. Do you know where the panel gets a voltage reading from? Also, where can I find a diagram of the relay box, mine is missing. I have ordered a service manual.
Any help is appreciated.