My car is randomly just shutting off.

Is it a US version 1984 Mondial QV?

When you say "the car just shuts off completely" does that mean:

1. the engine stops running and all the dash lights/gauges are "off" even though the key is "on", or

2. the engine stops running and all the dash lights/gauges remain "on" with the key "on"?

 

Yes, definitely sounds like a problem somewhere in the primary wiring. You wrote:

but your wiring diagram shows a more complex path of:

battery "-" terminal -to- 1st cable -to- battery cutoff switch -to- 2nd cable -to- chassis ground

Did you check/refresh all of this path (I'd certainly give the battery cutoff switch a few on-off-on wiping actions) or has you system been modified?

Same sort of thing on the "+" side -- wouldn't hurt to check/clean/reseat the "+" battery terminal and the A&B power connectors to the fuse-relay panel and the w white connector that goes to the ignition switch.

 

It may be the switch contacts, if the motor starts after turning the switch off and then turning the switch back through the start sequence.

If the motor has quit running, but the car is still moving, in gear and the clutch engaged, i.e motor is still turning but not running; try moving (wiggling) the switch without shutting it off and see if it starts running again. That would also indicate a corroded contact.

There is a thread on FC about removing the switch and cleaning the contacts with contact cleaner. CRC makes some contact cleaner that is safe for plastic. Some contact cleaner is not safe for plastic and will make a quick mess.

There may be sufficient vibration while the car is moving to enable the contacts to conduct electricity, but not when you slow down or stop.

Probably not a major component failure, but a connector, cable, or contact problem.

Good luck.

Jerry
DRG

 

Also, don't overlook the negative (ground) battery off/on knob, could be loose or corroded.
But it does sound alot like a loose electrical connection in the system.

 

+1 exactly what I was thinking.

 

Agree with a loose connection somewhere in the primary circuits off the battery incl. the cut-off switch.
Could a faulty cell in the battery itself create a similar issue in idle, when the alternator's output is low?
I remember chasing a similar issue on my 2CV years ago which was resolved with a new battery - very rough idle (and then you do feel that with a 2 cylinder boxer...) and occasional shutdown in idle but no problems at any other rpm. Just a thought.

 

I would check out the Battery knob and the big RED electrical wire from engine to front of car under the clutch slave cylinder.
My red plastic housing cracked and may loosen a good contact connection, sorry for the non technical term of what that is called.
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The ignition key contact was also my thought. When I was wrenching on cars we had a few come in. It was typically people who put a lot of keys on the ring and the stress/weight would wear out the contacts. You might be able to test without driving. Start the car and let it run then with a very light touch move the key, not rotating it but up and down, forward back and see if any of that causes it to die. On these cars as mentioned above, lack of use can cause corrosion in the unlikeliest of areas. Good luck.

 

Since it happens when momentum shifts to front in a stop
and
since you replaced the cables which could still be lose
did
you also make sure battery is locked in it's location.

seems the motion of the battery disconnects the lose connection.

 

I had that problem, and it turned out to be a burned connection at a wire into the fuse board. I think it was one of the ignition fuses, but I'll check tomorrow. I put a new wire
into the fuse board, and it worked. Prior to that, if I pushed in on that particular wire the car would fire right up. Ultimately, I changed the entire ****ing fuse board.

 

An entire fuse board may be an issue, but it sounds more like he can pin it down to a specific set of actions.

Fuse boards unless necessary can be expensive.

 

Agreed