Cuda dies in gear with headlights on

[Montclaire]

Hello, having an issue with my 74 Barracuda. Car runs and drives fine but dies out in gear when you turn the headlights on. It will stay running if you turn them on in park, and the lights are all bright - no flickering, turn signals work, etc. If driving it will run until it idles back down and then quits. It will not crank with the switch in the on position but will fire right back up if it's switched off.

I have replaced both battery cables, battery is good and the alternator is charging normally. I also replaced the high beam foot switch on the off chance that it was the problem but no change. Idle is set around 1,000 rpm. Ignition is mopar electronic with an older, USA made orange box. As I said it runs fine with the headlights off.

This is a fairly low mileage original car. I noticed that the headlamp switch is the earlier 70-71 style, so while it could be the headlamp switch, I'm thinking that was already replaced to try to fix the issue without success. I bought the car last fall and it had the same issue then (I'll try to pull the switch tomorrow and put an ohm meter on it).

One thing that might be important - the car has an older Mallory tach that's tied into the dimmer switch (gets brighter/dimmer with the switch). The dash dimmer switch itself works fairly well for the tach light but the dash bulbs themselves are spotty. Could it be drawing too much through the dimmer circuit? I wouldn't think that would be enough to kill the car but I thought I should mention it. This is a non-rallye dash car.

Thanks

[Chryco Psycho]

I doubt the mallory tach lights has anything to do with it but you could disconnect it & see .
I would have the headlights on realys , maybe ther is a problem in the firewall connector .

[1 Wild R/T]

I doubt the mallory tach lights has anything to do with it but you could disconnect it & see .
I would have the headlights on realys , maybe ther is a problem in the firewall connector .

[/b]

Exactly what I would suggest.... Headlights are drawing just enough power that when the car is in gear (which pulls the idle down slightly reducing the alternator output) that the voltage to the ignition module falls just below the critical threshold....

[dodj]

The only difference between park and drive is engine rpm, and nss position. Can't see the nss causing your symptoms so it must be the reduced alt  o/p when in gear....
Which means I agree with cp and wild. 

Take apart and clean all the connectors to eliminate small voltage drops.  Connector on red wire close to battery that feeds the interior, Column connector,  bullhead connector,  the connector by the passenger side valve cover.  Check the ecu and vr connectors.  Reassemble with dielectric grease. One or some of them are probably dirty enough or loose enough to cause a voltage drop.

[Bullitt-]

 I've never heard of anything like this.. once drove my '73 over an hour with alternator not charging to get home... battery was so drained after shutting it off it would not turn over the starter.   I even drove my Duster a few blocks with no battery in it, just running off the alternator
   You state "It will not crank with the switch in the on position".
Do you mean it will not engage the starter or that the starter turns but won't start?
 

[captcolour]

Make sure your voltage regulator has a good ground to the firewall.  I had to remove mine and sand the paint on the firewall to get a good ground.  Once I did that, headlights worked great without pulling down the idle.

[anlauto]

It will not crank with the switch in the on position but will fire right back up if it's switched off.

This is the part that confuses me...If the battery is good, why wouldn't the engine even crank over with the headlights on ? I understand the ignition maybe not getting enough juice to fire, but it not even cranking over ? How much juice are the headlights sucking, I've never heard of that before with a good charged battery.

Interesting problem...

[Montclaire]

Right, it won't even crank.  I don't know if the exterior lights stay on, but the interior lights do.  Car will not crank until I switch the lights back off. 

[Montclaire]

And since this is a 74 it has the goofy seatbelt interlock thing.  The reset is still under the hood.  The seatbelt retractor is jammed and I haven't gotten around to freeing it up - would that effect anything? Parasitic draw?

[Bullitt-]

Seatbelt interlock might explain the no crank situation but I don't see how the headlight switch could effect that....      On our '74 Monaco all I had to do to disable the interlock was unplug the sensors under the front seats. 

   

[Montclaire]

I'll make sure they are unplugged for the heck of it.

[PLY474]

You can try isolating the switch from the load.  In other words, unplug both headlights and try cranking with the switch on/off. 
Do you have the issue with just the parking lights on?

[Dakota]

My 2 cents on this topic:   this appears to involve a short in the headlight circuit.   I'd suggest taking a close look at the wiring feeding the headlights and the headlight switch to see if there's a spot with melted or cracked insulation.

When you try to crank with the lights on, do you hear the "click" from the starter solenoid trying to engage? Or nothing at all?  With a weak battery or a weak connection, most times I've seen you can at least get some clicking out of the starter system.

Hope you figure it out.

[Montclaire]

No click. Nothing. Will make a list and start ruling things out.

[Jim AAR]

Check your Reverse Light Switch and Headlight Foot Dimmer switch (and the ground), unplug them and try it.