Total power lost 1981 FI

[Montreal]

Hi
When we connect the battery, the clock works as the headlight etc.
When i try to start, there is even no cranking and we lose all electric power. No more headlights no more clock nothing.
Wait hours reconnect the battery: same thing. Light in dash are on, try to start, you loose everything.

Battery is good
Ground is clean to body.
Positive connection is good
Ignition key is new and connection are ok
We Replaced the double relay to eliminate that possibility.

We have also a 1978 carburetor, and it is much easier!!

What could we test ?
Thanks to all.

[ORFORD2004]

Connection at the starter?

[spider2081]

Sounds like a bad electrical connection. I would start at the battery and physically inspect the connections there. Remember bad connections often generate heat. So touch the connections if any of them are warm after attempting to start the car clean and tighten them.
At the starter solenoid the batter cable, a brown wire and a black wire's ring terminals all attach to the same post on the starter solenoid. The biggest green wire is the battery + connection, the brown wire brigs power to the ignition switch terminal 30 and the black wire connects the alternator output to the battery.
Under the hood on the driver side fender well area are 2 wire connections often over looked that cause intermittent starting ( the dreaded click) they are single bullet connections. One has brown wires and one has red wires. The brown wire is the same brown wire from the starter solenoid that powers the ignition switch terminal 30. The red wire is power to the solenoid when the key is in the "start" position from the ignition switch terminal 50. These single bullet connections are exposed to the weather and often corrode and become intermittent or bad. Look behind the alternator before the engine mount near the fender well to find them. pull them apart and clean them.

[Montreal]

Thanks
All connection a tight and clean
When i turn the key to run, dash works.
I turn to start and it’s shut down before cranking.
Now i put again to run, and there is nothing no dash no lights …

The only thing i notice is the double relay that was clicking for few seconds. And the. Nothing.

The only thing working is the clock and the hazard.

Very strange.

[Montreal]

Got it!
With all your good info
Bad ground from battery.
But it makes a very mysterious trouble.

Thanks to all!

[spider2081]

Got it! Bad ground from battery.

Great, Enjoy your ride.