1968 weird "stalls with headlights on" problem

Folks,

Been lurking since I got my GT/CS about a year ago, and I've seen the caliber of advice on this forum, so I thought I'd ask about this stumper:

I've got a strange problem with my 68 GT/CS - at night, with the lights on (park and head), she'll stall out (engine just dies like someone pulled the plug) at intersections, when backing out of a parking space and shifting into Drive to continue, etc. Seems to be tied to engine speed, i.e. it doesn't happen at cruise, on the freeway, etc. When it does happen, it restarts immediately (good thing, as I've been in the middle of an intersection waiting to turn when it's happened! ).

Previous owner put halogens in, so I added two relays (headlights/dashlights would shutoff intermittantly at idle before I did that, now they're rock-solid). The stall happens with either headlights on or Lucas fogs & parking lights, but not ever (so far) with just the parking lights on. I tried replacing the headlight switch, thinking it might be the circuit-breaker in it, but to no effect.

Needless to say, I can't drive it at night 'til I get this fixed. I don't want to start swapping out parts (coil, alternator, v-regulator, etc.) without some advice first. Anyone come across this before?

It's a 351W crate motor with a C4, new cap/rotor/plugs, starts/runs great (in the daytime), good groundstrap, wiring all looks good, etc.

Hoping someone can help,

Tom Warren
Phoenix, AZ

Can you tell us what your voltage at the battery is at idle with the headlights off and then with the headlights on? Are you running a high power stereo or anything else that would pull a lot of power (other than the halogens)? Try to duplicate conditions as closely as possible while taking your voltage readings.

Steve

Thanks, Steve. Will do as soon as my car comes back from the bodyshop (someone backed into my pass. side scoop a couple of weeks ago, and the parts just came in, so I should have it back in a couple of days. Moral of the story: when you're out in your classic and the wife asks you to stop and buy milk on the way home, say no :icon_no.

Although Steve (RVTrash) is your guy for this one...

I'll add my two bits. You have two circuits--the one to run the engine; points, plugs, etc...and then the headlight/taillight/fogs circuit.

It looks like the headlight circuit has some sort of problem where it's affecting the power to the points, plugs, etc.
(I know, that's obvious)...

So, for what it's worth, there may be something in the headlight switch that is shorting out the whole system. There also may be something in the turnsignal switch, and that (old) wiring on the steering column.

I think that a multi-meter reading on the headlight circuit, against the battery, and engine circuit will tell the story.

Steve can walk you though this, of course.

You have to remember that this 40+ year old wiring can crack and you'd have shorted out wiring in places you'd never expect. A meter can help isolate the problem.

For what it's worth--

Paul.

Thanks for the help, folks. I did some measurements yesterday, and it looks like the voltage drop from battery + terminal to 'BAT' alternator terminal is too high (.5-.6 volts), and it also appears that I have a 60A alternator in there. With my A/C, halogens, and Lucas fogs, it's too small.

Didn't Ford spec a 65A alt. for A/C cars in 68? Autozone and Checker didn't have one listed.

There are a couple of things I'm considering:

1) Rebuilding my alternator with a 'high-output' kit. Seen these somewhere on the net. Has anyone done this? Results?

2) If I can't find a stock 65A alternator, I may go with the GM 12SI 94A alt swap that some have done. Anyone had any experience with this swap?

3) Finally, I may just drop some major coin on a PowerMaster 1-wire alternator. I've seen some controversy on the web about 1-wire vs. 3-wire. My main concern would be idle, of course, since that's where my current alternator has a problem now. I don't know if the 1-wire would 'excite' at idle enough to drive all of my loads (A/C, halogens and fogs/floods). Don't want to spend the money only to have it not solve my problem. Again, has anyone done the 1-wire swap and run OK w/heavy elec. loads?

Thanks,

Tom

Let's start with your voltage drop. From the battery to the Bat terminal on the alt. is just wire with a couple of connections. If you're dropping voltage, you have a bad wire or bad connection. Buy some electrical contact cleaner and spray the 3-prong plug connection ends. Use some 4-0 steel wool on the connections at the solenoid and alternator. Make sure your positive cable is good, with no breaks or corrosion. If you still have a voltage drop, replace the alt. harness and positive cable. If you have resistance in the line, you will have increasing voltage drop as the load increases. You want to get to the point where both ends of the circuit are at the same level. As to the alternator, ask for an 80-85 amp unit from a '72 Mustang. Unless someone is leaning over your fender and reading the numbers off it, it'll look completely stock.

Steve

Steve is all over this stuff. I put a GM one wire on my car hoping to improve the low voltage characteristics. Especially the dimming of the dash lights when you put on the brakes or use the blinkers. No Joy. Seems the same and you do need more load or rpm to "excite" it to charge more. I have a volt meter not an amp gage and after warm up it runs low at an idle until you load it up or spin it up.

I am going to try LED's in the taillights. But I do not have stalling or even close. That is something else. Can't believe Neil has not weighed in yet. He likes electrical problems!!

Rob

Too wierd. Even if the alternator output is zero, battery voltage (11.5 volts, down to 9 or 10 volts) should still be enough to power the coil for ignition.
What is halogen current draw compared to the original incandescents??
How old, what condition is the Battery??
Good Grounds for Battery to Engine Block and to chassis??

These models run fine with normal operation - with 60A alternators (mine does), even running the A/C.
I DID install the LED's in the tail/brake lights, for less current draw, but primarily for higher intensity. But I had no electrical problems prior to the LED's.
Vewwy intewesting.

Neil

Could a combination of a weak coil and low voltage going to it generate such low output from the coil that it won't fire the plugs?

ALRIGHT darn it!!! Is this a "Lucas" Mustang?

Lucas? As in floods? Yeah, the later model Lucas Square 8 lights.

I'll go through it this weekend and clean all connections, sand/polish ground contacts, maybe replace alt wiring, etc. and see if it improves. Positive cable is new & longer, since I turned the battery 180 degrees to add a quick-disconnect ground for when I park it out in the open (and when working on the electricals).

I did order a rebuilt, high-output alt (90 amp) from Quality Power in Yucaipa, CA yesterday, just to ensure that I have enough idle amps to power everything.

With a 90A (max) alt, what guage BAT-to-solenoid wire should I be using?

I may try a new coil (inexpensive) just for grins. :smile:

Thanks for all the excellent advice, guys.

Tom

Update: I put in a new 90A alternator, with an 8-gauge wire to the solenoid, and scraped/polished/contact-cleaned all the connections in the loom, including the ground on the engine block - no joy. Still stalls after awhile w/headlights on, and almost immediately w/lights, A/C and fogs.

Tried a new Accel coil, with no change.

So I bumped the idle speed up a bit (to around 900RPM), and I can drive around town w/lights on and haven't stalled yet (need to try this again this evening).

I don't know what the real fix is, but is there an 'overdrive' pulley available (similar to underdrive accessory pulleys that allow you to reclaim some HP) that runs the alternator at a higher speed? or some other trick to get it to put out just a few more amps/volts at 'idle' to keep the damn thing running w/lights on?

I guess I could try a new battery, too, but it's never given me any problem before (starting, running, etc.), so I'm reluctant to just change it for no reason.

My last recourse is to take it to Salem Boys (our expert garage) and let 'em dig into it, but that's at a standard shop rate of around $75/hour, and could get really expensive, and lead nowhere.

:sad:

Tom

I would be curious to see what happens if you were to replace the halogen headlights with the standard incandescent headlights.

Neil

I thought of that, Neil. I may try it if the price for 2 standard lights isn't too high. Just for another datapoint. Even thought of going w/LED taillights to reduce that load, too.

Still, you'd think the system would be able to handle just the lights, even if halogen, with an upgraded alternator.

The pulley you speak of is actually larger to turn the alternator slower. Common on hipo 289 cars that spun a bit "faster". It will actually turn the alternator slower at idle and compound your problem in my opinion.

Can you isolate it to one accessory you pull on? Heater and wipers are ok. Wipers and fogs are ok? Intorduce one item and it has problems. A dead short on that system?

By the way, "Lucas" meant an "English" car with a "Lucas" electrical system! Famous for lots of electrical problems.


Rob

Rob,

Thanks. I understand how the underdrive pulleys work - I was alluding to an 'overdrive' pulley (if such a thing exists) to do just the opposite - run my alternator at a higher speed at idle as a 'fix'. Don't know if one exists (doubtful), or if anyone had seen one in a junkyard or interchange manual that has a smaller O.D. I've Googled for overdrive pulleys and only see serpentine/late model ones available commercially.

With just the lights on at idle, it takes awhile to stall, but it always will, usually in an intersection (at stock idle speed). With lights and A/C on (which also runs an electric radiator fan via a relay), it often will stall, and with lights, A/C and fogs, it'll die immediately. Looks like a combined load that kills it. If I rev it up to 1500 or so, it might stumble for a second when I switch on the fogs or A/C, but it won't die.

I'm going to try incandescent (old) headlight bulbs (if I can find 'em), and a new battery, and then I'm done. If that doesn't fix it, I'll stick with the faster idle speed and limit my night driving :sad:

Tom

Try the new battery first.

Neil

OK. New battery (Autolite Platinum, 700+ CCA, etc.) and it still stalls.

Here's what I _haven't_ done:

1) Voltage Regulator. Looks like it's fairly new (replaced by former owner?)
2) Pertronix Ignitor (in the distrib). Maybe it doesn't like <12.5 volts, or something. But I'm not going back to points!
3) Swap back to incandescent headlight bulbs (hard to find locally)
4) Taken it to a reputable shop and pay $75+ an hour for triage.

I guess #1 (vreg) is first, then the headlights (available on Amazon for $8 each), then maybe a newer Ignitor II or a call to Pertronix for possible diag steps, and finally #4 after I raid the piggy bank(s).



Tom

Tom,

Did you try to unplug the headlights and then turn the light switch on and see if it dies?

Just a thought. -Jeff

Jeff,

No, I haven't tried that. Since the only thing getting activated by the HL switch is the running lights (and it doesn't stall with just them on) and the halogen headlights, I'm not sure what that'll prove. But I'll give it a try later.

Right now, I'm going down the path of the Pertronix Igniter not getting enough voltage when the load is too high. I few web hits have shown that, while the Pertronix documentation says 'connect the red wire to the positive side of the coil or a 12v switching power source', they really meant to say 'unless there's a resistor wire going to your coil, in which case you need to connect directly to a 12v switched source'. One of their engineers posted a comment on how electrical resistance can build up as wires age, get hot, etc., leading to a substantial voltage drop to the Pertronix circuitry at idle.

Of course, mine's wired directly to the coil '+' post, so I'm going to reroute it to 12v off of the ignition switch (green/red wire, I believe), and see if that does it. Seems logical. :embarass:

Tom

For reference:

http://home.teleport.com/~cosa/vap/tech/pert/pertxhome.htm
http://www.calverst.com/articles/EL-Ignition-Pertronix_Ignitor_issues.htm