Turning on headlights cuts ignition

[Robbrob]

I had my car idling with the headlights on and when I came out a few minutes later the car was off and was flat dead, no cranking or clicking when I turned the key. I got it jumped and it idled for a few minutes  then started to stall until I pumped the gas then it would idle for a few more minutes. When I tired to turn the headlights on it was like the ignition got cut off. I got it in the garage and shut it off then tried to fire it back up and it was flat dead again. I’m pretty sure the battery is shot but I would think the charging system would keep it running unless it’s not working. I have it in a charger and will see what happens tomorrow. I would have it revved up and the headlights would still kill it. The headlights wouldn’t come on at all either when I hit the switch.

[Robbrob]

I know it sounds like a short of some sort but that sounds odd to me considering it was working fine a few minutes prior.

[maok]

Good chance that your battery is not holding any charge and/or your generator is not supplying enough current(amps) even when you increase the rpm.

 

Most generators will not supply enough current at idle, especially when switch your lights on.

[Sam Buchanan]

Agree. Probably defective battery and charging system due to either defective components or wiring problems. Need to spend some quality time with a multimeter. 

Edited May 8, 2023 by Sam Buchanan

[Sniper]

I don't know that the battery is defective what I suspect is happening is the battery is not being charged and when it gets drained down enough the ignition shuts off when the headlights come on. I would put the battery on a charger overnight and then see if it holds a charge.

[Robbrob]

I had a charger on it overnight, drove it up to the shop and was checking the wiring for the turn signals (another issue I gotta figure out) and I had the headlights on for about a half hour and it acted like it had a lot of power left and then all of a sudden it just lost everything, wouldn’t crank or anything so I threw a charger on it for a couple hours then it fired up and acted fine. Then later that night I fired it up again to let it warm up to drive home, that’s when my issues started. It acted dead again so I put it back on the charger and this morning when I took it off the charger it was still dead. The battery is a few years old and sat for awhile so I wouldn’t be surprised if it is shot.

[joecoozie]

Take the battery to an auto parts store and have it checked.

That would eliminate at least one possible cause.

[SteveR]

You might want to check the voltage with the lights on and running to see what charge is going to the battery.

[desoto1939]

I feel that you have a dead battery.  Did you pull the caps off the top of the battery to make sure that there is distilled water and or battery acid in each cell. Since you have a 51 mopar you would have a 6 volt battery. Did you check to see if the battery cable were clean and the battery posts were clean/ We had a similar situation at a car show last summer and gentleman drove his 53 Desoto to our show with no problems but when we got ready to leave the car would not start.

 

We checked everything then looked at the connections at the battery. We pulled the cable ends off the posts and we found acid corrosion on the inside of the cable end and on the post. Cleaned up the post and the cable ends.  We had to prime the carb a couple of time and finally the car started.

 

Also suggest that you put the felt washers on each post red and green and then spray the post with the battery protection spray.  Also go to the local autostore and get a battery hydrometer to test the electrolite in each cell.

 

I have a battery maintainer always connected to my 6 v battery in my 39 Desoto. If the cars are not running on a regular basis then the battery will lose some of its charging.

 

The battery is the life of your car so check them often.

 

Rich Hartung