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How do you measure 0.01 ohms accurately?

K

Klink

Regular Contributor
The test for the coils on my Johnson calls for a measurement of 0.1 ohms +-.05, Really? My $100 multimeter has an error of 0.2-0.6 depending on whatever. Do I go by the best reading? How close to the
0.1 ohms +-.05 does none have to be? It sounds nuts.​
 
With a digital meter?... Good luck with that. If that measurement is important to you for some reason, pick up a $8.95 (whatever they cost now) analog (needle) ohm/volt meter, connect the leads, zero it out and tke it from there.

However, I was never interested in the specified readings but more so interested in the continuity of the leads (as follows) unless the coil was cracked and shorting out to ground, in which case, it's bad regardless of the continuity.

If the continuity is bad/broken... either the coil will not fire, or if it does, it would be arcing out internally to do so.

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(Magneto Capacitance Discharge Coils - Continuity Test))
(J. Reeves)

Check the continuity of the ignition coils. Remove the primary orange wire from whatever it's connected to. It may be connected to a powerpack screw type terminal, a rubber plug connector, or it may simply plug onto a small boss terminal of the coil itself.

Connect the black lead of a ohm meter to the spark plug boot terminal, then with the red ohm meter lead, touch the ground of the coil or the powerhead itself if the coil is still installed.

Then touch (still with the red lead) the orange wire if it's attached to the coil, or if it's not attached, touch the primary stud of the coil. You should get a reading on both touches (contacts). If not, check the spring terminal inside the rubber boots of the spark plug wire. Poor or no continuity of a coil is one reason for s/plug fouling.

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(Battery Capacitance Discharge Coils - Continunity Test)
(Joe Reeves)
Remove the primary wire the screw type terminal. Remove the coil and unscrew the HT wire from the distributor cap.

Connect the black lead of a ohm meter to the HT wire, then with the red ohm meter lead, touch the ground wire of the coil.

Then touch (still with the red lead) the wire that normally attaches to the powerpack output lead. You should get a reading on both touches (contacts). If not, check the HT wire by unscrewing it from the coil. After removing the wire, the check can be repeated using the internal threaded prong within the coil instead of the HT wire. Poor or no continuity of a coil is one reason for erratic or no ignition and/or s/plug fouling.

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(Regular Magneto Coils - Continuity Test)
(J. Reeves)

Checking the continuity of the ignition coils....... Have the ohm meter set to High Ohms.

Remove the primary wire from points. Remove the coil ground wire. You do not want either of these wires touching anything.
Connect the black lead of a ohm meter to the spark plug boot terminal, then with the red ohm meter lead, touch the ground wire of the coil.

Then touch (still with the red lead) the primary wire. You should get a reading on both touches (contacts). If not, check the spring terminal inside the rubber boots of the spark plug wire.

If there is no continuity between the secondary circuit (spark plug) wire and the primary or ground, remove the coil from the armature plate, then check the continuity directly between the prong within the coil (prong that the plug wire connects to) and the primary and ground. Poor or no continuity of a coil (or plug wire) is one reason for weak spark, s/plug fouling, or no spark.
- - - - -
 
Don't even worry about the Ohms on the primary winding. If it is anywhere around an Ohm it is good (as far as the primary goes). That winding is hardly ever bad unless the external leads are broken.
 
joereeves said:
(Magneto Capacitance Discharge Coils - Continuity Test))
(J. Reeves)

Check the continuity of the ignition coils. Remove the primary orange wire from whatever it's connected to. It may be connected to a powerpack screw type terminal, a rubber plug connector, or it may simply plug onto a small boss terminal of the coil itself.

Connect the black lead of a ohm meter to the spark plug boot terminal, then with the red ohm meter lead, touch the ground of the coil or the powerhead itself if the coil is still installed.

Then touch (still with the red lead) the orange wire if it's attached to the coil, or if it's not attached, touch the primary stud of the coil. You should get a reading on both touches (contacts). If not, check the spring terminal inside the rubber boots of the spark plug wire. Poor or no continuity of a coil is one reason for s/plug fouling.
Click to expand...

My 1990 70hp is a Magneto CDI coil, I tested the coil loose off the engine , I tested it as you described and even switched black for red and all got the same reading 246 ohms
 
One of the little orange primary wires coming the power pack and going to the coil primary (the orange wire is part of the Powerpack and it connects to the coil with a boot) has a cheap blue butt connector spliced in between the Powerpack the boot, can you splice that wire like that?
 
Klink said:
One of the little orange primary wires coming the power pack and going to the coil primary (the orange wire is part of the Powerpack and it connects to the coil with a boot) has a cheap blue butt connector spliced in between the Powerpack the boot, can you splice that wire like that?
Click to expand...

Yes, sure you can... BUT... it's best to do it right via soldering the connection together and sealing it with a section of Heat Shrink tubing.
 
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