Does this Duraspark wiring need the ballast resistor?

Thanks

jbozzelle wrote:

Thanks

That depends upon a few things
Some Duraspark systems do not have a white retard wire.
IF the coil has .08 primary ohms or less, then it will need a ballast resistor for continuous running; for drag racing, short term usage, usually not.
Now if the coil has .14 primary ohms or more then it would not need a ballast resistor at any time.

Thanks Randy!

Any idea if the stock Ford TFI coil has more than .14 ohms?

jbozzelle wrote:Thanks Randy!

Any idea if the stock Ford TFI coil has more than .14 ohms?

The standard Ford TFI "E" core coil has only about 0.5 ohms.

Thanks. I'll pick up an MSD coil that fits the bill

jbozzelle wrote:Thanks.  I'll pick up an MSD coil that fits the bill

Just use a .85 ballast resistor or Pertronix and Accel make a high performance coil with enough primary resistance.

I have installed a MSD system on a 1979 460 and a 84 300i6 and never had to use the resistor. The 84 was a TFI system but I swapped the distributor for a late 70's duraspark.

The only reason I have ever heard that the resistor would be needed is if you can't shut off the engine. The MSD unit is getting feed back that keeps it running???

I have always used the rectangular MSD Street Blaster coil.

jones wrote:I have installed a MSD system on a 1979 460 and a 84 300i6 and never had to use the resistor. The 84 was a TFI system but I swapped the distributor for a late 70's duraspark.

The only reason I have ever heard that the resistor would be needed is if you can't shut off the engine. The MSD unit is getting feed back that keeps it running???

I have always used the rectangular MSD Street Blaster coil.

You heard wrong.
A ballast resistor is needed for continuous running with a FORD DURASPARK ignition so the unit doesn't get overheated when passing to much amperage because there is not enough primary coil resistance with the OEM coil which has .7 primary ohms.

rmcomprandy wrote:

jones wrote:I have installed a MSD system on a 1979 460 and a 84 300i6 and never had to use the resistor. The 84 was a TFI system but I swapped the distributor for a late 70's duraspark.

The only reason I have ever heard that the resistor would be needed is if you can't shut off the engine. The MSD unit is getting feed back that keeps it running???

I have always used the rectangular MSD Street Blaster coil.

You heard wrong.
A ballast resistor is needed for continuous running with a FORD DURASPARK ignition so the unit doesn't get overheated when passing to much amperage because there is not enough primary coil resistance with the OEM coil which has .7 primary ohms.

Learn something new everyday.

Are you talking about the MSD box overheating or the distributor? (I have always removed the duraspark box.)

PS. After looking at the wiring diagrams I wire mine differently so I guess I'll shut up and let tall have at it.

The coil overheats.

I'm learning something new here too. How does one check the ohms on their coil? My wife usually handles the electrical stuff.

cletus66 wrote:I'm learning something new here too.  How does one check the ohms on their coil?   My wife usually handles the electrical stuff.  

Remove the wiring terminals/horseshoe connector(Duraspark) from the coil, now using and ohmmeter attach one lead from the meter to the (+) side of the coil and the other lead to the (-) side of the coil, this will give the primary resistance of the coil. You can check the secondary resistance by removing the high tension coil to distributor lead, remove one of the test leads from one of the primary coil terminals, leaving the other test lead attached(doesn't really matter which one is left attached). Take the lead you removed from the primary side and insert it into the coil wire's female plug or attach it to the coil output's male terminal(depends on which type of coil you are using). The reading on the ohmmeter now gives the coil's secondary resistance measurement. Hope this helps.

Most meters have an ohm setting. I have an old Fluke meter that works. I would assume you put the positive to one side of the coil and negative to the other. That should tell you the resistance in ohms? (Am I close guys)?

Jones - I'm just putting a stock Duraspark box back into a car I'm putting together and didn't know if the ballast resistor was needed or not. Nothing fancy engine wise so I didn't feel the need to drop the cash on a whole MSD setup.

aquartlow wrote:

cletus66 wrote:I'm learning something new here too.  How does one check the ohms on their coil?   My wife usually handles the electrical stuff.  

Remove the wiring terminals/horseshoe connector(Duraspark) from the coil, now using and ohmmeter attach one lead from the meter to the (+) side of the coil and the other lead to the (-) side of the coil, this will give the primary resistance of the coil. You can check the secondary resistance by removing the high tension coil to distributor lead, remove one of the test leads from one of the primary coil terminals, leaving the other test lead attached(doesn't really matter which one is left attached). Take the lead you removed from the primary side and insert it into the coil wire's female plug or attach it to the coil output's male terminal(depends on which type of coil you are using). The reading on the ohmmeter now gives the coil's secondary resistance measurement. Hope this helps.

Thanks !! I'll check that out.

jones wrote:

Are you talking about the MSD box overheating or the distributor? (I have always removed the duraspark box.)

PS. After looking at the wiring diagrams I wire mine differently so I guess I'll shut up and let tall have at it.

NOBODY in this thread has mentioned an MSD box except you.
OEM Production FORD DURASPARK, (which is the wiring diagram shown here), is not near the same thing.