How can i test msd box and coil - Vintage Mustang Forums
 
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post #1 of 13 (permalink) Old 02-17-2019, 06:42 PM Thread Starter
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How can i test msd box and coil

Im having an electrical issue and need to test the msd box and the coil. When i test the box by arching the green and purple wire im not getting a spark. Im not even hearing the little buzz from the box.

Is there a way to test the box with out looking for a spark? Can i get a reading from the red and black wire that go to the ignitoin coil?
Thanks
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post #2 of 13 (permalink) Old 02-17-2019, 08:07 PM
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Are you getting voltage to the msd box? If you're getting a "buzz" from the msd box at any time you've got bigger issues.

Scott

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post #3 of 13 (permalink) Old 02-17-2019, 08:13 PM
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I think there are some you tube videos on the subject....
Seems like I remember seeing it.


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post #4 of 13 (permalink) Old 02-17-2019, 08:19 PM
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The MSD box has two heavy gauge wires (red and black) that need to be connected to the battery.
Two smaller gauge wires (orange and black) that connect to the coil.
And a smaller gauge red wire that gets switched on by the ignition switch.
With all those properly connected and the ignition on, you should measure 12v from the + side of the coil to a chassis/engine ground.

Shorting the green and purple wires won’t do anything. Those are for the trigger sense circuit and must be connected to the magnetic pickup coil in the distributor.

1970 Mustang coupe
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post #5 of 13 (permalink) Old 02-17-2019, 08:20 PM
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Quote:
Originally Posted by MrFlash View Post
The MSD box has two heavy gauge wires (red and black) that need to be connected to the battery.
Two smaller gauge wires (orange and black) that connect to the coil.
And a smaller gauge red wire that gets switched on by the ignition switch.
With all those properly connected and the ignition on, you should measure 12v from the + side of the coil to a chassis/engine ground.

Shorting the green and purple wires won’t do anything. Those are for the trigger sense circuit and must be connected to the magnetic pickup coil in the distributor.
Actually shorting those two is a way to test for spark. The coil should fire when the circuit is broken.

Scott

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post #6 of 13 (permalink) Old 02-17-2019, 08:51 PM
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Quote:
Originally Posted by Redneckgearhead View Post
Quote:
Originally Posted by MrFlash View Post
The MSD box has two heavy gauge wires (red and black) that need to be connected to the battery.
Two smaller gauge wires (orange and black) that connect to the coil.
And a smaller gauge red wire that gets switched on by the ignition switch.
With all those properly connected and the ignition on, you should measure 12v from the + side of the coil to a chassis/engine ground.

Shorting the green and purple wires won’t do anything. Those are for the trigger sense circuit and must be connected to the magnetic pickup coil in the distributor.
Actually shorting those two is a way to test for spark. The coil should fire when the circuit is broken.
However, you could use the white wire and hold it against a good ground. Pull the white wire off and you should get a spark.

1970 Mustang coupe
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post #7 of 13 (permalink) Old 02-17-2019, 08:57 PM Thread Starter
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When i put a screwdriver on the other end of the ignition coil wire, lay it close to ground, and jump the 2 wires i dont get a spark.
I should get an arch from the screw driver and usually hear a little zap. I need to get a coil tomorrow. Im looking for a way to know that the box is sending emergy to the coil
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post #8 of 13 (permalink) Old 02-17-2019, 09:00 PM
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Quote:
Originally Posted by wscott00 View Post
When i put a screwdriver on the other end of the ignition coil wire, lay it close to ground, and jump the 2 wires i dont get a spark.
I should get an arch from the screw driver and usually hear a little zap. I need to get a coil tomorrow. Im looking for a way to know that the box is sending emergy to the coil
Test for voltage at the coil.

Scott

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post #9 of 13 (permalink) Old 02-17-2019, 09:16 PM
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Apparently I didn’t fully understand the function of the MSD box.
Diagnosis instructions here:
https://www.holley.com/support/troub...ng_techniques/

Never too late to learn something new.

1970 Mustang coupe
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post #10 of 13 (permalink) Old 02-17-2019, 09:21 PM Thread Starter
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Should i get a constant reading or just just when i jump the green and purple
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post #11 of 13 (permalink) Old 02-17-2019, 09:22 PM
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I think there are some you tube videos on the subject....
Seems like I remember seeing it.


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post #12 of 13 (permalink) Old 02-17-2019, 10:23 PM
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Quote:
Originally Posted by wscott00 View Post
Im having an electrical issue and need to test the msd box and the coil. When i test the box by arching the green and purple wire im not getting a spark. Im not even hearing the little buzz from the box.

Is there a way to test the box with out looking for a spark? Can i get a reading from the red and black wire that go to the ignitoin coil?
Thanks

If you had a buzzing noise from the box and now it doesn't make any noise and you have no spark, the ignition needs to be repaired by MSD.

Nothing worthwhile is ever quick, cheap or easy, those that can't do, complain

71 Mach 1

HOLLEY TECH PAGES
FORD OE TACH HOOKUP FORD OE TACH HOOKUP w/MSD (pg 7)
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post #13 of 13 (permalink) Old 02-17-2019, 10:57 PM
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Quote:
Originally Posted by MrFlash View Post
The MSD box has two heavy gauge wires (red and black) that need to be connected to the battery.
Two smaller gauge wires (orange and black) that connect to the coil.
And a smaller gauge red wire that gets switched on by the ignition switch.
With all those properly connected and the ignition on, you should measure 12v from the + side of the coil to a chassis/engine ground.

Shorting the green and purple wires won’t do anything. Those are for the trigger sense circuit and must be connected to the magnetic pickup coil in the distributor.
The MSD boxes will not show 12 volts at the + side of the coil. Stock ignitions will.

'67 coupe, 390, 4spd.
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