Hi: I am a new owner of a 1922 Model T, I have had the car since November, My Dad had it 10 years prior working on it. I have a problem where it will not run on the mag setting, it will run great on battery but as soon as you switch to mag it stops. This started about 4 weeks ago, I started it to pull out into the drive and while it was at an idle it backfired and quit running, when I checked I found it had jumped the belt, I fixed that and tried to start it, it fired on battery but would not stay running when switched to mag. I have checked tie pickup in the top of the dog head and I have good juice from that when running, check the wires back to the switch and they are ok. Could I have a short inside the plastic case of the switch that will ground it out on the mag setting only?
If you have good voltage from the magneto, and a good wire to the switch, then the problem is more than likely in the switch. They are known for that.
One CAUTION: Make sure that you never fool around and mistakenly apply battery voltage to the magneto. This will de-magnetize the magnets, and you'll get nothing from the magneto until they are re-charged, which is a lengthy and difficult process. You will do well to disconnect the battery before doing any work at the back of the switch.
One easy way to be sure where the problem is, is to connect a wire to the magneto post, leaving the other end long enough to reach the "Battery" post on the coil box (but not connected). Then start the car on battery, and get it to a high idle. Switch the ignition switch to OFF, and immediately touch your jumper wire to the coil box post, being careful to do it in that order (see CAUTION above). If the engine picks up and runs, there is a bad connection somewhere, and inside the switch is your suspected problem.
Make a careful diagram of the wiring to the back of the switch before disconnecting them. You may need to put some identifiers on the wires, as the colors may have faded. The back of the ignition switch is probably held on by some bend-over tabs. They can be un-bent, and the back lifted off, and the contacts cleaned and shined. Sometimes the material the back is made of swells up and makes it difficult for the switch arms to make contact. You might need to rub the backing plate on some sandpaper to remove some of the swelled-up material, thereby allowing the arms to make contact. I'd suggest sealing it afterwards, to reduce moisture pickup and further swelling. Shellac might be good for that.
If your jumper-wire test does not work, i.e. if the engine will not run with a direct connection from the magneto terminal to the coil box, then it is apparent that your magneto is not putting out properly. Pull the terminal off the "hogshead" (remove 3 screws), and look inside. There is often a buildup of lint or other crud that inhibits the connection between the "needle" on the pickup and the blob of solder that it's supposed to stab into. If that connection is good, you may need to re-magnetize the magnets. Do a search on this Forum for the procedure. It involves a hand compass, and 3 auto batteries and a bunch of jumper cables.
Best of luck!
Thank you Peter: My two worst fears were the coil box was bad, or the magnets some how go de-magnetized, but since it does run on battery and I have good current out of the dog house I know that is ok. I think at this point I am going to get a new switch and install it, it seems to be the only thing I can not rule out.
What kind of switch is this ..... "Could I have a short inside the plastic case of the switch that will ground it out on the mag setting only?"
Should not be anything plastic in a model T switch.
Model T switch is all metal and can be disassembled to check the contacts inside. Shouldn't have to buy a new one. The inside parts are replaceable if required.
The switch guts are pretty rugged. You should be able to fix the one you have just by massaging the contacts a bit.
I have three Model T's. At some time each one of them did not run on mag. The first one the funnel on the oil line broke off and cut the magneto coils. I drove it for 10 years on battery. Fortunately I had an outside oiler. If I had known what was the cause, I would have fixed it sooner.
The second one ran on mag but cut out with a backfire. The problem was the ignition switch. I put in a replacement kit from one of the vendors and so far it has been fine since.
The third one, the magnets had moved away from the coils due to end play in the crankshaft. Fixed that and now it runs on magneto.
A sudden stop of running would most likely be a break in the circuit. First thing to check is the voltage output at the magneto plug. If it is OK, the problem would be in the external wiring from the plug to the coil box including the ignition switch. If no voltage or low voltage at the magneto plug, the problem would be internal. First clean up the plug and maybe you will get lucky. If that doesn't fix the problem, the problem is with the magneto itself and could be one of 3 things. Shorted or grounded coils, weak magnets, too much end play.
If you discover the switch is the problem, I'd recommend sending it to Ben Martin. Call him at 770-938-3376 for shipping instructions. He doesn't do e-mail, just phone and regular mail.
Like John, I wonder what kind of switch you have. If it has a plastic case it's not Model T. Here's what Peter described:
As he explained, if the backing plate has swelled and warped from moisture and lost contact, just rub it on sandpaper like this to make the surface even.
These Model T switches come in two flavors. One has the backing plate held in with pins, like this one, and the other has bend-over tabs. Otherwise they're all the same.
Watching with interest.
If you want to test the mag to see if it's working:
Hi I have not got back to the T, Just started a new job working nights. The switch I have in the car looks like the one Steve Jelf has but I an 90% sure mine is plastic, my Dad bought it from Mac,s I do know the rebuild kit number fro mac,s is 16-55632-1. I thank all of you for the input, I will get back to the car this week and post what I come up with. It is nice to know as a new T owner there is a place to get advise and learn more about them.
Not a good track record for the repro switches, I'll venture a guess it has Key # 55 ????
Ben Martin is the one for rebuilt Ford supplied switches. 1-770-938-3376
Ok. I got back to the T, taking the advice of Bob Jablonski, I checked for a short to continuity in the switch. With the battery disconnected I checked for continuity from the mag post on the dog head and the wire at the coil box. With the switch on battery I have no continuity, with the switch on off the same, but with the switch on mag I have continuity, that tells me the switch is good, but the car still will not run when on the mag side of the switch, on the battery side it runs great.Does any one have any idea's? also thank you Bob for all your help.
Your car will run on battery, so start the engine and run on battery. Then do the test described by Steve Jeff. If the magneto is good you should read over 6 volts AC. If less than 6 volts, the magneto has a problem. If the voltage output from the magneto is good, your problem is in the wiring between magneto and coil box.
When running on battery at idle and at "ABOUT" 1200 rpm what are your output voltages at the mag terminal.
You should see about 9 volts at idle and 25 or more volts at speed. At top engine speed you should have 29-30 volts or so.
Your switch on mag could have continuity but also a short to ground. To check this you will need to remove the mag wire from the hogshead .
I can agree with all that is said above. One area that should also be considered are the coils. If they are not set properly, there is a very good chance that the engine will not perform on both mag and battery. I had a weak mag (although it did put out) and had to detune the coils to approx. .09 so it would run on both mag and battery. My .02.
The can be a real "pleasure" to re-build with the available kits. I did 2 and in both cases I didn't/couldn't use all the new stuff. Both worked out but if you're not to savvy with this kind of stuff buy a repo from a reliable company.