[AT] tractor electrical question

[Howard Pletcher]

No, what he is reporting is just what should be happening.  With the
points open, no current is flowing through the primary circuit and there is
12V at the + side of the coil.  When he bumped the starter and closed the
points, the current flowing through the resistor in the primary circuit
results in a voltage drop so that there is now 6V on the coil as intended.

The wire from the starter to the coil does send 12V directly to the coil,
but this is only engaged while the starter is cranking in order to produce
a hotter spark for starting and is not connected to 12V  the rest of the
time.

The fact the coil seems to require 12V to its terminal when hot points to
an internal problem in the coil as discussed by Dell in the Yesterday's
Tractors article.

Howard



On Thu, Aug 26, 2021 at 2:53 PM Carl Szabelski <c.s.szabelski at gmail.com>
wrote:

>  By the way, I believe it’s not the coil and is related to the cranking
> motor. Especially since the voltage drops when you bump it like you said.
> Something in the motor may be partially shorted or corroded, causing a
> voltage drop to the coil. The coil should always see 12V whether or not
> there is a resistor, internal or external. The resistor is essentially
> after the coil winding and drops the voltage after the winding, not before
> it. If the engine is running fine when you directly connect 12V to the
> coil, the coil is working like it should and is good.
>
> Carl
>
>
>
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