Ignition issue

Dave H (MI) · Dec 9, 2012

I have my 1947 Farmall B, 12v conversion, in the shop. Was a runner but failed to start last Spring and has been sitting. I am running all my usual checks. Carb has been cleaned to get old gas out. Running continuity to make sure there is spark. I have 12v on both sides of the switch when turned on and also on the far side of coil. I have nothing on the near side terminal of the coil with points open or closed. Holding the center terminal of distributor near a good ground and snapping open the points does not give me a spark. I am thinking I need to replace the points and condenser but the lack of any voltage on that near terminal is confusing me. Should I have voltage on that side of the coil at some point? It is a new coil.

old · Dec 9, 2012

With the points open remove the wire on the side of the distributor. Turn the ignition on and hold the coil center wire close to the block then touch and pull the wire back off the side of the distributor stud. If when you do that you get a spark the insulator going in to the side of the distributor has cracked and is shorting out. Seen that happen many many times over the years so you either replace the insulator or pull the old one out and run a wire in its place then silicone the wire in place to keep water etc out

John T · Dec 9, 2012

With the ignition on there should ALWAYS be voltage (with respect to frame ground) on the hot INPUT (NOT to distributor) side of the coil.....

Over on the coils other OUTPUT terminal:

Hot battery voltage when points are open
ZERO volts when points are closed

Therefore if the engine is cranked over slowly a test lamp on the coils output (to distributor) should flash ON (points open) and OFF (points closed)

If the lamp never goes off (should when points are closed) the points arent fully closing or are burned/carboned severely and not conducting or the points or distributor isnt well grounded

If the lamp never comes on (and all else is okay), condensor is shorted or points are shorted out or remain closed or points or condensor wires are shorted or the distributors insulated side pass through stud/terminal is shorted or else the coils LV primary is bad/open

Work through this for more tips and diagnosis

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=farmall&th=5745

John T
John Ts Ignition Troubleshooting

John G. Hasler · Dec 9, 2012

> I have nothing on the near side terminal of the
> coil with points open or closed.

Is the coil getting warm? If not it is bad (with an open primary). If so there is a short to ground, either in the coil (in which case it is bad) or in the distributor (in the wiring or the capacitor).

Disconnect the coil from the distributor. Check for voltage at the coil terminal where the distributor was connected. If there still is none the coil is bad. If there is voltage there connect a jumper to that point and touch it briefly to ground. If you get a spark when you break that connection the coil is ok and your problem is in the distributor. If no spark the coil is bad.

Dave H (MI) · Dec 10, 2012

Thanks for the refresher! I have only been at this repairing end of things for about 5 years although I have been operating all this stuff for a lot longer. It all gets a little out of focus for me sometimes. The insulator was good on the side of distributor. Points OR condensor had gone south on me so I replaced both and spark is excellent. Tractor wants to start but doesn't. I have moved on to check other things...to be continued.

Ignition issue

Dave H (MI)

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old

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John T

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John G. Hasler

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Dave H (MI)

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