MTFCA Forum

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June 3rd, 2022
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I started this thread not knowing what I know now.... I used incorrect terminology and looked at the wrong things. But it all ended up for good, thankfully!
It ended up being a badly assembled switch. When I rebuilt the switch with a new backplate, the lighting contacts did not align properly and may have been shorting out the mag.
All i did in the end was disassemble, realign contacts, and reassemble. And now it works....
What follows is the journey i embarked upon searching for a good serviceable fix.
Many thanks to those that helped and encouraged me along the way.....
Best to all,
Dan
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(1rst post)
When selected to mag [red wire], the battery wire [yellow wire] has no continuity from the coil box input post [blue wire]. Correct me but I think that's correct.?????

When the battery [yellow wire] is selected at the switch, I am getting continuity to both the yellow battery wire and the red mag wire.

Is my switch screwed up? Is there a way I reassembled the switch incorrectly? Everything works but mag when the engine is running.

Looking at your excellent graphics it appears things are wired correctly, however, depending upon switch position, either MAG (only) or BATT (only) should have continuity to the center connection (blue-yellow wire) that connects to the ceramic post on the coil box. You don't want to apply DC current to the MAG as it can demagnitize your magneto magnets.

Have you tested the switch with the wires all disconnected to see if all contacts are correct? Unfortunately, with electric issues you just have to chase them down.

Hopefully one of our electronics gurus will chime in with better insights to your problem.

I did test the switch after cleaning and a new plastic back plate from Lang's. All was ok, so I thought before i wired it up and put it in the car.

I suppose worst case scenario is an eventual in the car recharge once we figure out the switch issue.
If I'm getting power to everything else wouldn't the switch guts be assembled correctly? Maybe I have one of the moving internal parts off a quarter turn or backwards.
I dunno..... I'll have to dig around unless somebody more knowledgeable can pull a rabbit out of the hat....
Thanks all for helpin'.
I just don't get how mag and battery have continuity when the battery [yellow wire] is selected at the switch. I am getting continuity to both the yellow battery wire and the red mag wire.

Testing the switch is best done with a battery indicator test lamp. That is sure way of knowing the contacts are performing their chores. Rock the key and the light switch knob to be sure each tested connection is firm, and that any wiggle won't cause the lamp to go dark

Dan, would a multimeter that sounds a continuous tone when continuity is achieved work as well as a test light?

I just don't get how mag and battery have continuity when the battery [yellow wire] is selected at the switch. I am getting continuity to both the yellow battery wire and the red mag wire.

Pic below is of my firewall.

It's gotta be in the switch.... I'll pull it all apart tomorrow and see what we find.

There are many different switch bodies taking different backing plates. I don't mean pin & clip on but Briggs & Stratton and Clum. Langs only sells repros for Briggs & Stratton bodied switches. Do the old & new backing plates match? By chance did you change the lock too? One other possibility - the backing places are designed to fit with the MAG screw at the 12o'clock postion - would help to see your parts

When selected to mag [red wire], the battery wire [yellow wire] has no continuity from the coil box input post [blue wire]. Correct me but I think that's correct.????? YES but this doesn't make sense then "Everything works but mag when the engine is running. So when selected to MAG you should have continuity to the Blue wire at the post - do you?
There really isn't much that can be wrong inside the switch, the small disk with contacts rubs across the backing plate. --
--
When the battery [yellow wire] is selected at the switch, I am getting continuity to both the yellow battery wire and the red mag wire.
There is no yellow wire on the switch its on the ammeter. Unless you meant the yellow / black tracer wire.

Thanks. I'll compare back plates tomorrow. I saved the old one.

I found that on the plastic back switch plates you can get trace metal on the plate. I solved the problem by using a dremmel cutting wheel to cut a groove across the track.

Did you lubricate the switch with anything but WD40

TRDxB2 wrote: ↑

Tue May 31, 2022 11:22 am

Did you lubricate the switch with anything but WD40

wd40 is not a lubricant. I do use a little silicone grease.

So......
I disconnected the blue coil wire from the post on the box ('26).
I then checked for continuity using my spiffy little radio shack digital multimeter:
1) Switch Off- all terminals on junction block are open. NO CONTINUITY.
2) Switch turned left for Battery- Gen and Batt closed. Continuity.
3) Switch turned right for MAG-
Mag closed. Continuity. Batt is open no continuity. The other 3 wires [lights] on the junction block are all closed and have continuity.

Tested from firewall block to blue coil wire on the post of the coil box:
1) Switch off- Mag and the 3 lighting wires have continuity.
2) Switch on MAG- Mag and 3 lighting wires have continuity.
3) Switch on BATT- all terminals on junction block have continuity to the coil box post.

***did not lube the inside of the switch. Reassembled dry.

Any ideas????

speedytinc wrote: ↑

Tue May 31, 2022 12:14 pm

TRDxB2 wrote: ↑

Tue May 31, 2022 11:22 am

Did you lubricate the switch with anything but WD40

wd40 is not a lubricant. I do use a little silicone grease.

I agree. Should have added in the lock - graphite should not be used in a Model T lock/switch

The car runs fine on BATTERY. But no MAG.
------>No lube in switch. Dry <-----

Here is a wiring diagram for a 1926. When you select MAG or BAT you are essentially selecting the source of voltage to the system. Your descriptions need to distinguish the position of both switches when you test continuity. The key is the switch that selects the input voltage and the handle selects the headlight choice: Off, Dim, On(bright).
So these descriptions are a bit fuzzy as to what switch positions are being referred to and what has continuity to what
Tested from firewall block to blue coil wire on the post of the coil box:
1) Switch off- Mag and the 3 lighting wires have continuity. <<<<This should not happen - no continuity for them to the blue wire when off
2) Switch on MAG- Mag and 3 lighting wires have continuity.
3) Switch on BATT- all terminals on junction block have continuity to the coil box post.

So to keep it simple for a starter car 1926
The key switch selects the voltage source for the coils - MAG or BAT
The handle switch select the the head light choice Off, Dim, On(bright). and uses the battery regardless of the key switch - this is possible by the brass bar between the two BAT screws on the backing plate. The outer screw makes contact to the light choice based on the handle switch position --
--
So the labels on the switch plate may be add so some confusion too. The key switch uses the labels with the red lines wile the handle switch uses the ones with the green lines

When I say "switch" in previous posts, I am referring only to the key. The light switch (green on your diagram) is off.

I don't understand how the mess can test one way with the blue wire off the coil box, and then test an entirely different way when hooked up properly.

What am I missing?

Who's the best wiring Guru on the board?

Professor Fate wrote: ↑

Tue May 31, 2022 4:12 pm

When I say "switch" in previous posts, I am referring only to the key. The light switch (green on your diagram) is off.

I don't understand how the mess can test one way with the blue wire off the coil box, and then test an entirely different way when hooked up properly.

What am I missing?

You need to look at the wiring diagram. For example the light contacts have continuity when the switch is in the off position because each of the light bulbs is connected to ground. Now, still in the off position, the magneto should not have continuity to ground, if it does then the magneto post is shorting out to ground, and can be the reason why it doesn't run on magneto. So disconnect the red wire at the magneto post on the Hogs head and test

Professor Fate wrote: ↑

Tue May 31, 2022 1:09 pm

The car runs fine on BATTERY. But no MAG.
------>No lube in switch. Dry <-----

Have you checked the magneto output at the hogs head? Also when you were testing for continuity, you didn't state the point to point so to me all that was meaningless. There are Model T guys in your area that should be able to help you out. You aren't that far from Lang's for excellent technical support.

Haven't checked output of mag.

When testing point to point I went from blue coil box lead to junction block. Only difference was whether the blue lead was connected to the coil box post or just to multimeter lead. Power from battery was always off during testing.

When you go just to the terminal strip, and probe let's say, a lighting circuit...if I understand you correctly, you state that you then have continuity to the MAG wire (red) at the barrier strip.

Let's look at the circuit(s) you just connected to...touching the lighting circuit (black) on the barrier strip, that path goes through the bulb to ground...the same ground that is attached to the mag winding and goes through the mag winding to end up at the barrier strip (red). You just proved that your meter works...unfortunately setting it to "beep" is not the way to use it for this function...you in fact just measured two circuits in series, with no switch in the loop. That's why you are showing "continuity". If you looked at the meter each time it "beeped" you would see different OHM readings which would correspond to each circuit or in this case the totality of resistance in two circuits tied end to end. It seems mysterious, but is not at all.

touching the test leads together while on a very low OHM setting and then "zeroing" the reading on the meter (read the manual to see how it is done on your particular meter) will prepare the meter to take accurate OHM readings of each circuit...in the case of the MAG coil to ground, the OHM reading is exceedingly low, but it does have some resistance, and if the meter is carefully zero'd you can and will be able to measure it.

The tests you want to be doing are both isolation and ground testing. Have a look here: https://www.freeautomechanic.com/wiring ... s%206.html

I've read and reread your test methodology and your results and think that what you are describing in some cases is not how I would describe the same thing, so there are almost certainly some misunderstandings between you and the readers of the forum. My description above regarding the lighting circuit having continuity through the mag ring is one example of that...

I would bet that you do not have the problems that you think you have, but time will tell.

[/quote]
"......the magneto post is shorting out to ground, and can be the reason why it doesn't run on magneto. So disconnect the red wire at the magneto post on the Hogs head and test
[/quote]

Will try asap. Thanks!

Magneto coil has only .5 OHM resistance and thus can appear to be shorted to ground when in fact it is not. Shorting to ground is a possibility, but among the scenarios for it's failure that is a low probability one. There are a number of reasons why a magneto may not work and lack of function is not a certainty that it is the coil's fault. In any event, shorted or not, it has no bearing on the results you're getting when using the "beep" function on the meter.

Keep a methodical approach to your electrical testing...disconnect the wires from the barrier strip so that you do not accidentally test multiple circuits at once like I mentioned above. You have already checked the switch with wires disconnected and if I understand your results, your switch functioned correctly, so that's a start. If that's the case, then any problem you have is in the loom coming OUT of the barrier strip (I'm not certain you have a problem at all, but that's still TBD). Do your isolation/ground testing on each bare/unhooked wire. There are so few wires it will only take a minute or two.

Good Luck

Dan, the actual switch in your photo has the back plate turned 120 degrees too far to work properly.

The best way to verify the contacts are correctly set is to assemble the switch with all the screws removed and look in the screw hole for a shiny copper connector.

Then the screws must be short ones so they don't try to twist the contacts.

The blue wire goes in the center terminal, but if the insulation on the terminal is pushed back, it could be shorted to the small metal strip and be on all the time.

Here is one I did recently.

Note the extra screw with no wire attached.

A magneto needs a ground to turn it off.

A wire to ground is required on that screw, if your engine is running with a Magneto, like a lot of early tractors used.

Then the engine stops when the key is turned to Off.

Ground vs. No ground.

Why does one depiction say "optional? (GREEN WIRE) "

Professor Fate wrote: ↑

Wed Jun 01, 2022 7:03 pm

Ground vs. No ground.

Why does one depiction say "optional? (GREEN WIRE) "

Artist call. There is no reason to ground the combo light switch. Some switch’s have a GRD terminal, but that was used in testing only, as noted in a Service Bulletin, no Ford had such ground wire.

Going to rig up a bulb tester next.

Professor Fate wrote: ↑

Wed Jun 01, 2022 7:03 pm

Ground vs. No ground.

Why does one depiction say "optional? (GREEN WIRE) "

Grounding the switch plate would only be necessary if the switch had a dash light or lighted ammeter and the natural metal to metal connections were lacking a good ground at the switch plate. Some owners mounted a dash light on the rectangular ignition switch but there is no room an a '26/7

That Ground was also required for an Accessory Magneto to stop it making sparks and shut down the engine.

J1MGOLDEN wrote: ↑

Thu Jun 02, 2022 1:02 pm

That Ground was also required for an Accessory Magneto to stop it making sparks and shut down the engine.

You got me to look closer to the switch backing plates for that "extra" screw. So here is the something I had not paid much attention to.
The current images on Lang's site show no GRND screw on the clip type but one on the PIN type
You will also notice that the OFF position on the Clip type just has an indent while the PIN Type has a brass contact from the GRND screw --
--
However. I had order several backing plates during the past year and have a stash I need to go through. The one's from Lang's have no GRND screw but the PIN type looks to have a place holder for it. I did order on from Bob's about a year ago and he had just one, an older repro. It has the GRND screw.
So point well taken - If you have an accessory magneto you either need an ignition switch with the GRND screw or a separate switch that grounsds the MAG when its turned off

So I made up a test light to run a lead from mag post to light per the John Regan design using an 1156 bulb, and a lead to ground. Ran the car on BATTERY.
And whaddahyahknow....... the light on the mag post glows briliantly! So it's not the mag.

Further investigation to follow!

Professor Fate wrote: ↑

Thu Jun 02, 2022 9:51 pm

What should I look at next????

In review "When the battery [yellow wire] is selected at the switch, I am getting continuity to both the yellow battery wire and the red mag wire. "
So here is something to try. Isolate segments of the wiring by disconnecting the mag/red wire from the terminal strip
Disconnect the mag/red wires from the terminal strip and each other
With the switch OFF test the continuity of each red wire separately to ground
--What is the continuity of the switch red wire to ground
--What is the continuity of the red wire to the mag post and ground
Next with the switch set to BAT test the continuity of each red wire separately to ground
--What is the continuity of the switch red wire to ground
--What is the continuity of the red wire to the mag post and ground
Next with the switch set to MAG test the continuity of each red wire separately to ground
--What is the continuity of the switch red wire to ground
--What is the continuity of the red wire to the mag post and ground

Professor Fate wrote: ↑

Thu Jun 02, 2022 6:32 pm

So I made up a test light to run a lead from mag post to light per the John Regan design using an 1156 bulb, and a lead to ground. Ran the car on BATTERY.
And whaddahyahknow....... the light on the mag post glows briliantly! So it's not the mag.

Further investigation to follow!

Mag is working, but as you increase RPM the bulb should blow.

Excellent news

Excellent news and then some!!!

We ALL learn from things like this. Glad you solved it.