Trouble diagnosing magneto failure. Following from older threads, I determined that my magneto post point was too short, thus not contacting. Had another available, which I've proven does contact (well less than 1 ohm resistance). Per Ron Patterson's older descriptions elsewhere, I was sort of shocked to see that my Mag does output reasonable voltage and passes the described light bulb test with surprisingly good brightness, which brightens further with engine acceleration. But alas, when I switch to Mag, it doesn't work! I tried a Mag "connectivity test", suggested by a Model T person (tested resistance between Mag post and the connection at bottom of coil box; this turned out to be well less than 1 ohm, thus passing that test, I think). Have a 1926 Tudor. Checked the wiring connections ; all sound and correct (wiring harness is new). Any suggestions where to go from here?
When you did a resistance test between mag post and the connection at bottom of coil box were all the coils removed? If not you could be reading though a coil and the timer to ground.
Have you checked the switch?
1) Coils were all in the coil box. Have to do that again, then.
2) Didn't 'check' the switch (other than to make sure the coil wire was properly and securely attached to it). How to check / what to check on the switch?? Other than get a new switch and see if new one works?
If you check the resistance from the mag post to the connection at bottom of coil box (with the coils out and the switch in the MAG position) you have checked the wiring and the switch all in one step. If you don't get continuity, then check the wiring and the switch separately.
How to check the switch: run a continuity (resistance) check through it. With the switch set to MAG, see if current flows from the MAG terminal (red) to the COIL terminal (blue/yellow).
Thanks Steve me too having low output so from this
print I can grab terminal #2 for a voltage check
so I dont have to remove the floor board.
terminal #2 Red
If the car runs on BAT but not on MAG, the blue/yellow wire from the switch to the coil box has to be good. That leaves only the red wire and the switch,and their connections.
Aha, Does NOT pass the connectivity test with the coils out of the box. Car does run on BAT, but NOT on Mag. Looks like switch is the most likely culprit. Re-checked wiring, and its properly connected. Wiring harness is new.
Upon opening the switch you may find that the back plate, made of something like Masonite or heavy cardboard, has become warped so the contacts don't contact. Rubbing it on a sheet of coarse sandpaper will level the surface and polish the contacts.
Just a warning here that you must be very very careful while you are probing around that you do not accidentally short the magneto red wire to either of the 2 battery wires that are next to it on that barrier strip. Terminals 1 and 3 both contain hot battery power all the time while the magneto red wire is between them. If you accidentally touch any source of battery power to the magneto red wire or magneto post it will discharge the magnets in your engine and kill the magneto or seriously weaken it. Go slow and careful and to be safe, lift off a battery cable while you are playing with the switch and magneto wiring.
Magneto now Works! Did as Steve Jelf noted in picture above (I had old pin type switch, which wasn't in car -- in car was a newer clip type -- I switched them and sanded the back plate as Steve recommended, thus cleaning the contacts and planarizing it, and low and behold, Mag now works!!) Thanks all who commented!