Car dies when I turn on the lights

mhsprecher

mhsprecher

Well-known member
I have a fairly new problem that I have just started to diagnose. When I turn on the lights, the car dies. It doesn't happen all the time, but most of the time. My car is a 6v with a Powermaster alternator. It charges at 6.5-7 volts when running. If I turn the lights off, it will start again easily. The fuse on the starter doesn't blow.

I looked at the light wiring and it looks okay. I took the light switch off at the bottom of the steering column. Everything looked okay. I cleaned it up and reinstalled it. It is a repro light switch, probably at least 20 years old. I also loosened and retightened the ground. I have a second ground to the transmission, too.

I took a look at the headlights. If I take one bulb out of either side, the car doesn't die when I switch on the lights. Sometimes if I turn the lights on, the ammeter registers a discharge and the alternator reads it is charging at 5v and the engine misses. It will then die sometimes.

One thought is that I need a ground in the headlights, but I have not had this problem until last month. I am a bit stymied at this point. Any ideas?
 
Last edited:
Look in the ignition system. Measure the voltage at the coil when the lights are turned on. If the voltage falls much below 6 volts then there is some resistance in the wiring for the ignition, such as loose or corroded connection. If the voltage is OK then you may have a bad coil or other part of the ignition that is marginal. Check the points to see if they are conducting well. Check for other sources of resistance, such as the ground strap. Do you have a second ground strap for the battery that goes to a transmission bolt?
 
Sometimes if I turn the lights on, the ammeter registers a discharge and the alternator reads it is charging at 5v and the engine misses. It will then die sometimes.
Click to expand...

Sounds like an alternator problem or an alternator not grounded properly problem.
 
Try undoing the "yellow" wire going from your cut-out to the bulb "switch" for your headlights. That should cure the dying.

And proves out the issue is WITH the headlight circuit.

Sounding like a "short" in the headlights somewhere. Might even be in the stop light switch which when you're messing with the lights you're likely to have your foot on the brake.

You could even provide a 6v (-) supply from a separate (+ grounded) battery directly to that yellow wire and then cycle the headlights and see if that affects the car.

Check out the Wiring Diagram. https://sacramentocapitolas.org/2017/10/18/model-a-wiring-diagram/

Joe K
 
Mshprecher,

What is the age and state of charge of your battery? If the battery is adequately charged, the car should start and run with the lights on for a significant amount of time without the alternator charging.

With headlights on, ignition switch off, turn the engine over with the starter for 10-15 seconds. Do the lights go dim? If so, the battery is at a low state of charge. This combined with loose, corroded or otherwise faulty connections (high resistance) can cause the primary ignition circuit to be unable to saturate the secondary winding of the coil. This means poor or insufficient secondary circuit spark to run the engine.

You said you loosened and tightened the ground connections at the frame, but that really isn't enough. All connections, ground or otherwise should be clean, bright, metal to metal, especially the ground connection at the frame. Use sandpaper and/or wire brush. Do the same for both battery connections.

Clean and tighten the connections of the battery cable at the starter switch stud, the safety fuse, the terminal box, the coil, then the connections behind the instrument panel.

If you own a copy of Les Andrews blue book, "Troubleshooting and Diagnostics", Chapter 2 has a logical sequence of quick and easy voltage tests to assist in isolating the cause of this sort of problem.

I hope this helps.
 
Last edited:
Just for giggles, by pass the starter mounted fuse, after a time those crappy made fuse holders can go bad, I’am thinking your loosing voltage through the holder. All electrical connections need to be clean and bright and tight ( thanks to Tom Wesenberg for this saying
 
Do you have the old style headlight connectors? They maybe touching each other and are hard to notice. I like to use the butt connectors in the headlights.
 
The original poster has a fuse next to the starter switch, which does not blow, so the chances of a short in the headlight wiring is low. Most likely resistance in the wiring somewhere, a bad battery, or marginal ignition component. All can be tested with a voltmeter.
 
Thanks for all the comments. I hope to get back to the problem in the next few days.

The battery is a couple of years old. I will have to see when I bought it. I have no trouble starting it.

As nkaminar said, I have a fuse on the starter (how did he know that?) I will do the diagnoses from the Les Andrews book. i will also swap out the alternator with a recently redone generator to see whether it may be in the voltage regulator. The brake light switch is another possibility I will look at. On my other car, I was blowing fuses at the starter often and it turned out it was the brake light switch, which had gone bad.

Oddly enough the problem started at Hershey after I cleaned up the light switch at the bottom of the steering column when I had the car judged. I had been driving the car around Hershey at night without a problem, but on the way home after the show on Friday, the problem exhibited itself. Maybe just a coincidence.
 
msprecher, X2 on Neil's reply #2 and #10 and Ted's reply #7.

About a year back, our coupe failed to restart on a gorgeous summer day. full sun and 98 degrees with 90 percent humidity. Battery was in the process of failing, but it still started the car. When I disassembled the connections at the starter switch stud, I found the components to be oily, dirty and soaked with coolant from an earlier leak. After cleaning just that one connection, the car fired up on the first compression. It was almost as if it was a small explosion.

Sometime soon thereafter, I measured the battery electrolyte with a 12$ hydrometer. The middle cell was found to be just above the red range. A combination of a low but usable battery and a dirty connection was likely lowering the voltage to the ignition. Cleaning the one dirty connection allowed the systems to operate, but things were not back to normal with a battery that had a cell running just above the red range. After trickle charging the battery for a couple days, the cell had not recovered. I replaced the battery.
 
I don't know much about the Powergen alternators other than they are made to look like a generator. Normally, an alternator will take up a good amount of slack that the battery may not be pulling. I'm not sure how this type alternator self excites. The GM 10si needs either a GEN light connection to a battery or it needs an elevated rpm to self excite and start charging. The alternator's internal electronic control unit should increase amperage output instantly when the system needs it. Voltage output should be a constant 7.2 volts but I know that the converted GM/Delco 10si units are all set to 7.8 volts constant which is a bit on the high side for a 6-volt battery. I don't know about the Powergen.

Keeping ground pathways clean and tight is a must for any electrical system. I learned to use silicon dielectric grease on connections early in my aviation maintenance career. Some folks think a dielectric will stop flow but in a tight connection, the grease is pushed out of the direct contact and the bit that pushes out helps prevent corrosion and keep moisture out. We also used it in magneto distributor cap terminals to prevent arc over of high tension voltage. My preference is Dow Corning DC-4.
 
You said it yourself, in the first post: " The fuse on the starter doesn't blow."

LOL. I read through it again and missed that.
 
Hello, also make sure you have good ground to both engine and body , although not original I run both a ground cable to engine and also body from a master switch to the battery.Sometimes on restored cars the painting is so through the ground to lights and electrical are insulated.
 
I bought my car in 2008, a '30 Tudor. From the gitgo, when I turned on the light switch, the car would miss. It has a rebuilt 6v generator with now a diode cutout. I have done everything suggested above over the first ten years. New battery, new coil, checked voltages AT the coil.... replaced the wiring to the headlights and added grounds to each light on the car; disconnected the dash light. Replaced the headlights internal sockets with new from Brattons; I have a fuse on the starter but have changed that when it looked dirty. Voltages are all up to snuff and being an electronic enthusiast, I have always been stumped on this. How did I fix it? I switched to LED headlight bulbs and the problem has never recurred in four years.
 
Voltage out of generator is determined by what battery you have (6V or 12V). The only adjustment on the generator is the current (Amps). If no load from the battery, the generator voltage can approach 40 Volts.
Still think the problem is in the lighting circuit or horn.
 
mhsprecher said:
Thanks for all the comments. I hope to get back to the problem in the next few days.

The battery is a couple of years old. I will have to see when I bought it. I have no trouble starting it.

As nkaminar said, I have a fuse on the starter (how did he know that?) I will do the diagnoses from the Les Andrews book. i will also swap out the alternator with a recently redone generator to see whether it may be in the voltage regulator. The brake light switch is another possibility I will look at. On my other car, I was blowing fuses at the starter often and it turned out it was the brake light switch, which had gone bad.

Oddly enough the problem started at Hershey after I cleaned up the light switch at the bottom of the steering column when I had the car judged. I had been driving the car around Hershey at night without a problem, but on the way home after the show on Friday, the problem exhibited itself. Maybe just a coincidence.
Click to expand...

Hello Milford. Any chance you may have tweaked something when you were cleaning the light switch? If the wiring is old, maybe there is a thin spot somewhere on the harness is shorting out from possible wire movement during the cleaning. Yes, I know it’s a long shot but from my personal experience, some of my sudden car anomalies resulted from the last thing I did. You will find the culprit in time. Best, Steve
 
You must log in or register to reply here.
Back
Top