MTFCA Forum

Place your bets: is it the headlight socket, the switch or something else?

I noticed that I have a complete loss of electrics, and the engine stalls when I turn on headlights... sometimes. It is reproducible. I can idle the car in my driveway, and flip the lights on and off, and eventually the engine will stall.

When I have the driver's side headlight unplugged I don't have the issue. I can flip the switch all day long without issue with the tail light and passenger light plugged in.

The wiring from the switch all the way to the light is all new, the plug is new, the bulb is new, and all that is left to replace is the socket. A new socket is needed either way because the contacts are frustratingly loose and the bulb and plug slowly work away from each other, even after some gentle bending to provide a tighter fit. A new socket is coming in this week from chaffin's.

I'm not smelling smoke, and I have a 25 amp fuse at the starter switch post. Ground seems good within the light housing but I don't have a dedicated wire to ground the bulb. Right now I just rely on the contact from the socket to the housing. I had the socket out once and wire brushed it and where it touches the housing.

So is the culprit most likely the socket, the switch or something else? We should be able to eliminate the socket from the equation when the new one comes in. Thoughts?

Socket. If you can't reproduce the fault with it unplugged that is the culprit.

Disconnect all the headlight wiring from the terminal block and on the back of the switch. Start the car and see what If the car stalls again then there are other issues.

Yes. I'm troubleshooting the mag at the moment.

BHarper wrote: ↑

Sun Jul 30, 2023 9:28 am

Are you running the car on battery?

Yes. I'm troubleshooting the mag at the moment.

So, adding the bulb and turning it on slowly kills the engine but doesn't blow a fuse...

I cannot imagine that there is a direct short to ground then, as the fuse would blow if there was and everything would die immediately if running on BAT.

Slowly running out of poop indicates a decent draw on a dead battery or a really bad ground from battery to frame. The ignition system requires VERY little amperage to run but a headlight added may very well overwhelm a running car that has an essentially a dead battery (or a really horrible ground at the battery)...if the generator is set to 4-5A as is reasonable for a T, it will not keep up a dead battery that is also running lights as it will be a net discharge and continue to deplete the battery resulting in poorer and poorer ignition until it dies.

From your complaint, I wonder if it is THAT bulb causing the problem or the new CUMULATIVE draw that installing that last bulb causes.

I'm going to stick my neck out and say that once the socket is changed and all is "good" it will still die and then removing the OTHER bulb would have the same net effect of removing the present bulb

do a discharge test on the battery OUT OF THE CAR and at least rule it out...if it's good, then disconnect the ground wire at the light (from its excellent ground) and ground it directly to the battery (taking the ground strap out of the equation). The bulb may well have a good ground to chassis, but chassis has lousy ground to the battery... and report back that my advice was either spot-on, or just another WAG.

I’m confused by something here. You are running the car on mag you say. I ASSUME (dangerous word), that the lights are connected to the battery?
If you are trying to run the lights on the magneto, they require a special high voltage low amperage bulb and they should really only be used when driving at some speed.
I can see that a LED bulb might be a good option.

Les, I agree with what you said, but I think you are misinterpreting the MAG thing:

Are you running the car on battery?

Yes. I'm troubleshooting the mag at the moment

from that exchange, I understand that he's running on battery

Hi Dan,
Just to pin this down, disconnect the mag wire at the post so nothing gaes wrong. run a jumper ( wire with aligater clips) from the yellow
wire on the terminal block to the coil box ( blue/yellow tracer) Start the car & repete the headlight install. if it stays running then look @
switch or wiring to it. I would also try a smaller fuse if you do have a short it should have blown.
Craig.

Well said Harper.
For Model T’s issues can be over thought out and made more convoluted than they really are by thinking in todays technology and trying to solve them that way.
Trial and error and starting with the most obvious thing first usually works every time.
Checking the battery first and then following the lighting wiring second sound like the best direction to begin with.

Thanks for all of the replys. I'll try an answer across the board here. I'm focusing on the headlight/stalling issue at the moment, and have been treating the mag issue separately. For the mag issue, there is a wealth of information on mag problems here and I'll work through those posts first. If I get stuck I'll create another thread after I build the testing rig with a light as described in other posts.

I assumed I should be able to run on battery with the lights on. I get a reading of around zero amps when I have the lights on with the engine at running speed. I'm hover around 7 amps with the lights off.

The battery was bought in the early spring and wasn't used until about a month ago. It produces 6.5v disconnected from the car. I have a multimeter but no other battery testing tools.

The bulb in the light now is new, and the same issue occurred with the older bulb. The older bulb is out of the picture now, as it broke while messing with all of this.

The car doesn't slowly die, it just cuts out all at once.

I'll try grounding directly to the battery when I get a chance to pull it.

BTW, the double pin light sockets are out of stock at Langs, Snyders, MACs, and Smith & Jones. Chaffin's had them but they confirmed that they are struggling to order more. You may want to pick them up from Chaffin's while you can.

Can you start this engine on a starter? It is possible the battery is not completely charged. Try a 6 volt charger on the battery while it is running with both lights on and see if it still kills the engine. If it stills while on the charger, you have something wrong with the battery. Even the ground could be bad. Clean up the terminals and the chassis where the ground terminal is connected. The copper strap grand works better than the braided ground cable.
Norm

Norman Kling wrote: ↑

Sun Jul 30, 2023 6:01 pm

Can you start this engine on a starter? It is possible the battery is not completely charged. Try a 6 volt charger on the battery while it is running with both lights on and see if it still kills the engine. If it stills while on the charger, you have something wrong with the battery. Even the ground could be bad. Clean up the terminals and the chassis where the ground terminal is connected. The copper strap grand works better than the braided ground cable.
Norm

Norm,

It starts easily on the starter. A quick tap and it's humming away. I will try the charger idea and I'll clean the ground and terminals. I have the braided ground at the moment.

For tonight I disconnected the battery from the car and threw a 6v charger on it. We'll see how it behaves tomorrow.

Question
When the engine stalls and dies do the ignition coils still buzz or have enough current to buzz?
And on the other hand is it getting a good fuel flow after it stalls?

If you hadn’t mentioned it being an electrical issue the stalling and sputtering description would be very similar to a fuel issue.

Arbs wrote: ↑

Sun Jul 30, 2023 7:58 am

Place your bets: is it the headlight socket, the switch or something else?

I noticed that I have a complete loss of electrics, and the engine stalls when I turn on headlights... sometimes. It is reproducible. I can idle the car in my driveway, and flip the lights on and off, and eventually the engine will stall.

When I have the driver's side headlight unplugged I don't have the issue. I can flip the switch all day long without issue with the tail light and passenger light plugged in.

The wiring from the switch all the way to the light is all new, the plug is new, the bulb is new, and all that is left to replace is the socket. A new socket is needed either way because the contacts are frustratingly loose and the bulb and plug slowly work away from each other, even after some gentle bending to provide a tighter fit. A new socket is coming in this week from chaffin's.

I'm not smelling smoke, and I have a 25 amp fuse at the starter switch post. Ground seems good within the light housing but I don't have a dedicated wire to ground the bulb. Right now I just rely on the contact from the socket to the housing. I had the socket out once and wire brushed it and where it touches the housing.

So is the culprit most likely the socket, the switch or something else? We should be able to eliminate the socket from the equation when the new one comes in. Thoughts?

In review:
1: This problem is using your battery not the magneto to run on
2: The engine only stalls when you turn the headlights on...sometimes
3: When the driver's side headlamp is unplugged you don't have the issue and can run all day without any problem
4: The contacts in the driver's side headlamp socket are loose

Have you wired the car per the attached diagram based on your components?
The switch can not be the problem since it controls both headlamps in parallel from the terminal block. Since you don't have the problem when the driver's headlamp is unplugged, the problem must be from the terminal block driver's side connection to and including the driver's side headlamp socket. Like you said.

I wouldn't bother doing anything until you replaced the driver's side headlight socket to see if that's all that needed to be done.

You have been replacing wires and harnesses. What kind of shape are your headlight wires in and how is the switch?

I've been using Ron Patterson's wiring diagram. All the wires are brand new from the switch to the headlight. The only difference in my system is that I've eliminated the horn for now.

The switch is older, maybe original?

Fuel flow seems fine. Carb is rebuilt as well. Fuel tank flushed, steady flow to carb.

When the socket comes in, I'll swap it and test. More to come!

I suspect that the wire entering the socket is grounded by a defective socket and when you unplug it, the ground disappears. With the wire connected directly to ground through the defective socket, you ground the output from the battery and generator. Only question is, Why doesn't the fuse blow? The new socket should correct your problem.
Norm

Norman Kling wrote: ↑

Mon Jul 31, 2023 10:54 am

I suspect that the wire entering the socket is grounded by a defective socket and when you unplug it, the ground disappears. With the wire connected directly to ground through the defective socket, you ground the output from the battery and generator. Only question is, Why doesn't the fuse blow? The new socket should correct your problem.
Norm

I agree 100% with your assessment and have the same question about the fuse 25 amp vs 20 amp

So the consensus is that there is a dead short in the socket when the bulb is installed...

16 gauge can safely carry 13A maximum and at some point of overload beyond that, it will burn (based on specific temp rating of the insulation, which I do not know)

by deduction from the above though, we can determine that the full potential amperage of the battery is dumping straight to ground but never exceeding the 25A value of the fuse and the wire is not burning or smoking.

Perhaps my logic has failed at some point here, but the whole "shorted socket" thing is hard for me to believe

Now, I do know that a typical safety factor in wiring a given circuit is to limit the total load to 80% of the wire's rating, being that I am not an electrical engineer, I do not know the actual anticipated amperage failure point of 16 gauge stranded wire, though. Regardless, the description of the problem includes a statement that no burning can be detected, and again, a 6V automotive battery dumping to ground (and not through the light bulb's element) is most certainly going to blow a 25A fuse or the wire will die trying.

It will be interesting to hear the final result...troubleshooting/testing the socket should be a very quick test and not involve replacing to accomplish the test...simply inserting the bulb and checking resistance from input to ground will tell the tale

Isolating each element of the circuit and doing ground/isolation testing should take all of 10 minutes

The new socket seems to have worked. My son (9 years old) installed the new socket, with some direction, and we can't recreate the issue. I flipped the light switch many times and we just kept on ticking away. We even went to Ritas with the car to celebrate! He loves explaining to the onlookers which fixes he was responsible for.

Thanks again to all who chimed in.

Excellent!

especially nice to year about that boy's pride and excitement

glad it all worked out and that it was as simple and direct as you thought

The gremlins are back!

Everything seemed like it was working until it wasn't. I turned the lights on again and the whole car shut down, while I was on battery. I switched to mag and drove home without issue.

Even though it was frustrating, this time the battery side of the car was consistently dead when I turned the lights on, so I could really debug it. I took a multimeter and started tracing the issue from the battery forward. I fully expected it to be the switch.

I went through this process with the light switch off and on...

Battery, good.
Starter switch, good.
Fuse and connections, good.
Terminal block connection, good.
Power to ammeter, good.
Power to switch, good... until I turned the lights on.
Went back to the ammeter, and the post connected to the switch was dead.

Tried it a few more times and consistently the ammeter post would be where voltage would drop to zero when the lights were on.

I swapped out my original, nice looking, ammeter with one of the repro ones the vendors have. Luckily I had it lying around. Now the headlights are solid.... and brighter!

The original ammeter wasn't dead and would display amps while the engine was running.

The headlight socket did need replacing, because the headlight bulb could not make a good connection but I think ultimately it was the ammeter.

With all of the parts going into it, my 1923 car is slowly becoming a 2023 car. This should be the end of my electrical issues... wait, what's that...