Turn headlights on and engine cuts off!

[detmatt]

Not the Imperial but one of my B-bodies.
I can pull the switch out so that all the running lights are on front to back but when I pull the switch out the rest of the way to turn on the headlights the engine cuts out immediately. '71 Dodge Charger R/T.
Any guesses?
thanks in advance.
i would have gone over to FBBO to pose this but I greatly respect all on here and there's far fewer of you. I like smaller crowds

 

[polara71]

Since I dont have a test light any information I will give would be a guess :2204040-xmaseek9_gi

 

[commando1]

The draw from the battery when you turn on the head lights kills the juice you need to keep the engine running. The alternater has crapped the bed. And you don't need a test light to come up with that diagnosis.

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[1978 NYB]

The draw from the battery when you turn on the head lights kills the juice you need to keep the engine running. The alternater has crapped the bed. And you don't need a test light to come up with that diagnosis.

(Sent using Forum Runner)

Wouldn't hurt to have a cheap multimeter to measure the alternator ouput and voltage in general and continuity checks.

 

[detmatt]

I'll check it out first thing in the morning, its right outside my bedroom door.
thanks gents, kinda what I was thinking even though its a new one.

 

[1978 NYB]

I'll check it out first thing in the morning, its right outside my bedroom door.
thanks gents, kinda what I was thinking even though its a new one.

How old is the battery?

 

[detmatt]

Not a year and its a red cap.

 

[commando1]

How old is the battery?

Yes. Use a float tester and check! EACH cell.

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[1978 NYB]

Ok, have to look at the entire charging circuit which includes the battery.

 

[bluefury361]

Not a year and its a red cap.

A quick and easy way to check alt output is to start the engine and then disconnect the pos battery cable....should stay running. If not the alt is likely at fault, need to check further.

 

[1978 NYB]

Not a year and its a red cap.

Is it a gel cell battery?

 

[detmatt]

Testing voltage at battery with engine running at idle its 13 volts, rev it up and it hits 14.2. Should be over 15, right?

 

[Wildaugust]

Well to me, 13 volts @ idle with all lights and accesories turned off seems a little low. If it was 14.2 @ idle that would be perfect. IMO It should stay in the 14 - 14.7 range with lights and accesories off.

 

[detmatt]

Pulled the alternator and took to the parts store to test, along with a couple of others I had laying around and the one that was on the car tested good.

 

[mdh157]

Testing voltage at battery with engine running at idle its 13 volts, rev it up and it hits 14.2. Should be over 15, right?

that's not bad..........might be a little low, they taught us in tech school that 13.6 was right @ idle. did you try shutting the switch on all the way while revving the engine to see if it holds?

sounds like either a bad alt or maybe a corroded wire stifling the flow......it should be holding at 12.6 or above during load, and it's not, so it may very well be the alt. if it's not the alt, perhaps the switch is bad and is pulling too much when fully extended.

 

[bluefury361]

Pulled the alternator and took to the parts store to test, along with a couple of others I had laying around and the one that was on the car tested good.[/QUOTE

]

Take a good look at your pos battery cable and the link cable as far as8-10 inches back from the battery. I've found cables corroded inside of the insulation in that area. Also the lead connection lug at the alt.

 

[moparpaw]

Well Matt ....what was it..............a loose ground???

 

[detmatt]

I honestly don't know, I got busy with some more important things and then Christmas is happening so it went on the back burner till later this week. I will keep you updated though.
thanks for asking.

 

[1978 NYB]

I think the headlight switch is bad. The car runs fine otherwise.

 

[detmatt]

Sounds good too, doesn't it?