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Farmall & IHC Tractors Discussion Forum
Show Parts for Model:

Re: testing a 12 volt coil

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Author  [Modern View]
John T

05-22-2014 10:18:31
216.249.72.121



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A low energy low voltage simple ohm meter continuity test can show if a coil is definitely BAD but it cant tell you if its GOOD. IE If it fails its bad but even if it passes it may still be bad.

The resistance of the LV primary between the small + and - terminals should be around 2 to under 4 ohms (many around 3) but if its an open circuit the coil is BAD.

The resistance of the HV secondary should be in the vicinity of 3000 to under 10,000 ohms and again if its open its BAD.

HOWEVER it can pass BOTH those but still be bad due to HV breakdown especially once warmed up.

If the switch is good if you place a test lamp on the coils output (To distributor) terminal and crank the engine over slowly, it should flash ON and OFF which simulates when the points opened (coil fires and light is on) and when they close (coil conducts current lamp is OFF)

You can also bench test a coil and use a plug and plug wire and each time after the coils LV primary conducts current but then its interrupted (like points opened) it should fire.

John T

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