Troubleshooting Magneto

[ModelTMaryland]

Hello!
I wanted to ask if anyone has run into a similar running issue. We're having trouble figuring out the cause of our running problem.

We have a 1920 Touring.

After replacing my ignition switch with the reproduction switch and a Ford amp meter, the yellow wire from the starter switch began to smoke; I disconnected the battery within a few seconds. The yellow wire from the starter switch to the wire terminal melted and hot.

I replaced the electrical wiring on the driver's side, including the yellow wire and the ignition switch wiring. I also installed an aftermarket amp meter that originally came with the car when we purchased it and removed the Ford Amp Meter causing the short.

With the reproduction switch and the aftermarket amp meter, the car was no longer shorting. However, this is when my issues started, as the car would not engage the low gear on Magneto.

I installed the reproduction switch and new wiring, but now the car cannot engage low gear while on magneto. It will run and drive on battery, and it will idle on magneto, but once you engage low gear, the car will stall. Also, the car can drive on Magneto in reverse.

We took voltage measurements on the magneto using an analog meter and bulb:
The magneto at Idle is at 10 volts. Quarter down on the throttle, and the magneto climbs to 15 volts. The bulb gets brighter as the volts and rpm increase. However, engaging in low gear causes the car to sputter and die, even after warming up the car.

We checked the coil boxes. They're running perfectly, which we verified with a coil tester, and the spark plugs are getting spark.

The crankshaft end play is fine.

The car's engine and transmission were rebuilt in 2017 by Lilleker Antique Auto Restoration.

I have run the car on battery, and it doesn't stall when engaging the low or high gear.

I am inclined to try another ignition switch and see if it resolves the issue. I am also considering recharging the magnets.

Would it be possible that the electrical short I had before caused the issue with my mag even for a few seconds?

Thanks for any feedback or help!

[RecklessKelly]

If the contact pad of the mag is clean and mag post is making good contact onto it, I would question the switch for a short or bad conductivity. Try hot wire from mag post to coil.

[Dan Hatch]

Maybe battery short though the mag?
You better check your wiring and also recharge magnets.
Add the fuse to the power wire?

[speedytinc]

Repop switches are notoriously bad.
I worked on one with the center switching contacts having 1 of the 2 attaching rivets missing. It shorted against the switch body when the contacts shifted.

In this situation I would bypass the switch & connect the mag wire directly to the coil box input. Retest for a change in symptoms.
CAUTION: Make sure there is NO POSSIBILITY of DC voltage to get to the magneto, it will kill the mag.
Dont do this if you dont completely understand the electrical system.

Its possible that a repop HH mag contact/oiler is not making consistent contact from a weak spring.
If the above bypass test dosent solve the issue & thats a repop contact, look @ it as a possible source.
The moral of the story: Repop parts have a much higher failure record.

[Jerry VanOoteghem]

Have a look inside the switch. If a short fried your yellow wire, you have to wonder if anything inside the switch got fried as well. Really though, blaming the switch ignores the symptom of stalling when on mag and engaging low band. If you run the engine at a high idle and feather in the low band, so as not to slow the engine much, can you nurse it along without stalling? Also, can you take a mag voltage reading while running and engaging low? I'm really believing that your short somehow got some battery voltage going to the mag. Maybe just enough to weaken the mag sufficiently at low RPM's, (like when engaging low band), to kill your ignition.

[ModelTMaryland]

Have a look inside the switch. If a short fried your yellow wire, you have to wonder if anything inside the switch got fried as well. Really though, blaming the switch ignores the symptom of stalling when on mag and engaging low band. If you run the engine at a high idle and feather in the low band, so as not to slow the engine much, can you nurse it along without stalling? Also, can you take a mag voltage reading while running and engaging low? I'm really believing that your short somehow got some battery voltage going to the mag. Maybe just enough to weaken the mag sufficiently at low RPM's, (like when engaging low band), to kill your ignition.

I'll take a look inside the switch.

I will also attempt to run the car at a higher idle during low gear.

We looked at the analog volt meter while on magneto and engaging low gear and the voltage was dropping as I pressed down on the gear pedal to low gear until the car died when i fully pressed the pedal.

I am wondering if the battery may have gotten into the mag.

[Moxie26]

Could it be the contact points in the generator cut out are stuck , being the cause of your burned wires ?

[ModelTMaryland]

Could it be the contact points in the generator cut out are stuck , being the cause of your burned wires ?

The generator has a diode cut out, so I don't think it's stuck. It's a good thought, though!

[ModelTMaryland]

Repop switches are notoriously bad.
I worked on one with the center switching contacts having 1 of the 2 attaching rivets missing. It shorted against the switch body when the contacts shifted.

In this situation I would bypass the switch & connect the mag wire directly to the coil box input. Retest for a change in symptoms.
CAUTION: Make sure there is NO POSSIBILITY of DC voltage to get to the magneto, it will kill the mag.
Dont do this if you dont completely understand the electrical system.

Its possible that a repop HH mag contact/oiler is not making consistent contact from a weak spring.
If the above bypass test dosent solve the issue & thats a repop contact, look @ it as a possible source.
The moral of the story: Repop parts have a much higher failure record.

I will look into this option.

[Mike Silbert]

Something that is occasionally occurs and will cause lots of headaches is the wiring connections. These harnesses are hand made and good quality but every once in a while things go wrong. After the melt down it got some new wiring that has also not been proven. Verify that the wire end terminals are properly installed and tight.
To speed up the troubleshooting process repeat the bulb and meter test on the coil box input terminal. It is supposed to be the same as the magneto post readings. If it is the same then the wiring and switch are all proven to be ok. If not, then work through the system to find the issue.
Mike