Re: c farmall electrical

Posted by Tom on October 30, 2003 at 22:17:38 from (205.188.208.73):

In Reply to: c farmall electrical posted by jf on October 30, 2003 at 13:07:28:

Jf,

Here's the deal. You should have battery voltage on the positive side of the coil. The negative side of the coil is actually wired to the points with a small wire that goes from the negative side of the coil into the distributor. You can see that wire inside the distributor and you should see that it is connected to the post on the points. The other side of the points is always at ground potential since that side of the points is actually bolted to the metal base (the distributor plate) of the distributor.

When the points CLOSE, you have a complete circuit from the battery to the positive side of the coil, through the coil, through the wire to the distributor, through the closed points to ground. With that completed circuit, current flows through the coil and charges the primary winding of the coil.

When the points OPEN, the current flow is interrupted and the magnetic field within the coil collapses, inducing a large voltage into the secondary winding of the coil. This large voltage is presented to the big wire that comes out of the top of the coil and is delivered to the center post on the distributor. The rotor inside the distributor delivers the large voltage to the spark plugs via the spark plug wires.

The condenser, by the way, (also called a capacitor) is across the points. That is, one side of the condenser is also bolted to the distributor plate just like one side of the points, and the little wire coming out of the condenser is attached to the post on the points where the little wire is coming from the negative side of the coil. The only purpose of the condenser is to absorb the voltage spike that is generated when the points open. This keeps the points from arcing excessively and burning the points. Your engine will actually run okay without any condenser installed, but the points will arc and burn out much more quickly.

Okay, so you say that you have "current" to the negative side of the coil. I assume that you actually mean that you have battery voltage on both the positive and the negative side of the coil. If that is what you mean, it indicates that the points are not closed. That's okay if the points are OPEN due to their being on one of the high lobes of the cam inside the distributor, but is not okay if the points are on a low lobe of the cam. When the points are on the low lobe of the cam, they should be closed. When they are closed, you should have zero voltage on the negative side of the coil.

Now, what to do? First, make sure that the wiring I have described above is okay. Then, turn the engine over so the points are on a LOW lobe of the cam inside the distributor (that means the points are closed). Leave the ignition switch on and check the voltage on the positive and negative sides of the coil. You should have battery voltage on the positive side and no voltage on the negative side. Now turn the engine over slightly so that the points are on one of the high lobes of the cam. You should have battery voltage on BOTH sides of the coil.

If, when the points were closed, you still had battery voltage on both sides of the coil, it indicates that the wire to the points is broken or the points are not closing properly. Fix it.

If, when the points were open, you didn't have battery voltage on both sides of the coil, it indicates that the coil is open, the little wire running from the negative side of the coil to the points is actually touching ground somewhere, or the condenser is shorted out. If that is your situation, turn the key off and remove the wire on the condenser where it attaches to the terminal on the points. Turn the key back on. If you still don't have voltage on both sides of the
coil, you have a short to ground in the wire to the distributor, the points are so badly out of adjustment that they aren't opening, or the coil is open.

I've been messing with cars for more than forty years. I've very seldom seen an open coil and I've never seen a bad condenser. That doesn't mean they don't fail, it just means that they aren't likely candidates. Usually, the points are bad or a wire is either broken or shorted to ground.

Hope this helps a little.

Tom

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• Re: Re: c farmall electrical jf 02:59:32 10/31/03 (0)

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