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Another Duraspark Question.
#1
Been a couple years since I wired up a duraspark. But if I remember right I wired the white wire to the S terminal on the solenoid and the red wire to the I terminal. I metered those last night and have 12 full volts so that should work correct?? 12 volts on S when cranking. 12 volts on I when key is on.

Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
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#2
Are you using a 'cheater' harness from NPD like I did?  If so, you might run into the issue when the engine only runs while cranking.  I think I wound up hooking them both up to the 'I' terminal and not worrying about the 'cranking advance' feature.  There might be something in there that's not quite right, or I grabbed the wrong keyed source, or something stupid like that.

When I went through later and hooked it up according to Mustang Steve's directions, I wound up smoking my first Duraspark box (ran fine for awhile, then just quit running... to never run again).  I put it all back, got a new box, and it's been fine ever since.

Not much help here... I just wanted to be part of the conversation.    rofl

Eric

[Image: mach1sig2.gif]
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#3
Thanks Eric.  I have wired a few of these over the years. I did not buy the harness. I make my own. But I think it will work just fine going off the I terminal for power. Gonna be few days till I can test fire. Still waiting on fuel line fitting and carb spacer.

Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
  Reply
#4
The connection from the "I" terminal on the solenoid to the coil is connected to the wire running from the ignition switch to the coil after the pink resistor wire. If you still have the resistor wire in place the wire at the "I" terminal will show 12 volts until the coil is loaded (the negative side is grounded by the points or Duraspark box) and then will show the reduced voltage of 6 or 7 volts. The only time the "I" terminal supplies the full 12 volts to the coil is when the solenoid is energized and powering the starter.

Use this wiring diagram from Mustang Steve

[Image: durasparkfinal.jpg]



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#5
Why was I reading 12 volts at the I terminal with just the key on?

Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
  Reply
#6
Because the coil is not loaded, and not drawing the voltage down through the resistor wire. The voltage through a resistor shows full battery voltage until a load is placed across it. The "I" terminal is being back fed from the wire that runs from the ignition switch to the coil.

This illustration shows the effects of loading on a DC circuit

[Image: boe2-4-2.gif]

With the ignition switch on, ground the negative terminal on the coil and then check the voltage on the "I" terminal.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
  Reply
#7
(02-23-2019, 09:19 PM)Don C Wrote: Because the coil is not loaded, and not drawing the voltage down through the resistor wire. The voltage through a resistor shows full battery voltage until a load is placed across it. The "I" terminal is being back fed from the wire that runs from the ignition switch to the coil.

This illustration shows the effects of loading on a DC circuit

[Image: boe2-4-2.gif]

With the ignition switch on, ground the negative terminal on the coil and then check the voltage on the "I" terminal.
 Thanks for the explanation Don! To do your test will I need to have power going to coil also?? I don’t have it hooked up yet. So put my meter ground on the negative of coil and Check the I terminal with key on?

Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
  Reply
#8
Yes, the ignition wire would have to be connected to the coil.

To correctly wire a DuraSpark follow the diagram from Mustang Steve, or get a harness from one of the vendors. The feed for both the DuraSpark and a performance coil must come directly from the ignition switch, bypassing the resistor wire. You can feed the stock coil from the resistor wire, but you still need a full 12 volts for the DuraSpark, which must come from the ignition switch or from the battery via a relay.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
  Reply
#9
Thanks for the help Don. You are correct. I checked voltage while cranking then idling. It drops to around 7 volts. So I got under the dash and bypassed the resistor wire and now have 12 volts while running. Seems to be working good! Thanks for the help! Now to finalize the wiring and hide everything.

Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
  Reply
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