Duraspark

[djburton]

On an original Duraspark ignition setup,specifically a 79 Mustang 5.0, does it allow for 12v to coil in start position,dropping voltage in run? A guy calls me up,says it won't start. I checked coil + lead voltage in start,5.5v,no start. Ran a 12v jumper to the lead,starts and runs with jumper removed. Any thoughts? Have the schematic but print too small to read. Thanks!

[Chuck]

Duraspark 1, No resistance wire to the coil. The spark box would turn off coil power if the distributor wasn't turning or you weren't cranking so it wouldn't burn it up with the key on.

[Rory428]

Chuck, what years were Duraspark 1 used? On my 59s 428, I am using a Duraspark distributor from a 75 or 76 Ford PU truck, and a "Blue" strain original Motorcraft Duraspark ignition module and coil. I currently have the ignition power source going thru the 59s original external ballast resistor  , that was used with the points ignition. The engine fires up quickly, cold or hot, and runs well, but when I took it to the dragstrip, it just felt lazy as the revs got near 5000 RPM, so I decided to bypass the ballast resistor with a temporary jumper wire, and the engine ran much better, and picked up 6 tenths of a second in the 1/4 mile. Not sure if running the full 12 volts to the coil would hurt it`s reliability over time, so I went back to using the ballast resistor for normal driving, and using the jumper wire to bypass the resistor at the track. Just curious if I could run the Duraspark at full 12 volts without concern or not.

[Chuck]

I believe that dura-spark II came around ‘76 or ‘77 and has the two and four wire connectors. Dura-spark I had the coil wire power come from the box on a three wire connector. The distributor needs to spin to turn the coil power on.

[427Fastback]

I have done countless Duraspark conversions since Ford SVO made the harness in the 80's. I have always run them full 12V and never had a failure. The last one i did on the 66 Mustang Fastback with the 428CJ I got a painless wiring harness.It came with a resistor so i wired it up. Car started fine..This is a ongoing subject with no real answer. I always use blue strain Motorcraft boxes..I have half a dozen FE Duraspark dist..I will continue full 12V till I see a failure..JMO....Cory

[djburton]

Update...This thing would not start with 5v to the coil when cranking. The problem ended up being they were using a remote starter switch. Since there is no (I) terminal on the relay,12v to the coil on start has to come from the harness. Remote switch didn't work,you need to use the key switch to get 12v to the coil in start, and then measured around 8v in run.

[MeanGene]

Every time I see one of these threads. I come away more confused lol. Some say full 12V to coil, some say resisted, around and around. I am trying to restore my 65 F100, which is on a 79 F150 chassis with a 400. When I got it, the PO had installed one of those POS and ugly-assed aftermarket HEI conversion dizzys. Started really well, stumbled off idle, ran OK once it got rolling, got me home, about a half hour. To further complicate it, it has one of those Chinese replica Holleys on it, which seems to be functioning OK. The HEI started running on about half the cylinders, and has quit completely. It came with a box full of Duraspark parts, a fresh aftermarket dizzy that had been in the 400, a blue module and an aftermarket module, original coil with the horseshoe and bracket. He said it had run OK but had a problem and he had swapped the dizzy and it turned out to be something else. I have several MSD boxes and my intention was to go that way with the MSD conversion harness, but could also go with the blue Duraspark module. So- will the original 65 resistor ignition wire work, or not? 12 volts to either box, but resisted to the coil, or? To make thing worse, it has fresh alternator (Delco) and regulator, and was delivering 16V instead of 13-14V, didn't keep running long enough to check that out, but thinking I need to change the regulator. BTW, I also have two original Durasparks from 460s, one from a Colony Park wagon for sure, the other from a friend, might go with one of those instead of the aftermarket unit, after a recurve

[427Fastback]

I do have the wiring schematic I got back in the 80's with the Ford SVO duraspark wiring harness. I will dig it out tomorrow and scan it. They do not say anything about a resister. I have had the same blue strain box in my 68 since the mid 80's..Not saying I am right but I have never had a failure in 40 years and I have a huge pile of Duraspark stuff for a reason. I always fire mine of the I terminal on the solenoid.... Cory

[Lowrider]

Years ago I converted a Yblock distributor to run a Duraspark system. I was surprised how much better it ran with the conversion.

[427Fastback]

Here is the schematic that came with the Duraspark harnesses that I bought from Ford........Cory

[Rory428]

Thanks for the wiring diagram Cory. On my 59, with the resistor in place, the car started and runs great, in normal driving, but  was weak at higher RPM, which was eliminated when I bypassed the resistor, and went to full 12 volts. Cory, curious what coil you have been using with 12 volts, I have been using factory Duraspark coils that use 2 flat top studs, and the plastic horseshoe connector from the donor car.

[427Fastback]

Hey Rory...generally use a MSD blaster 2F. It has the correct terminals for the horseshoe clip..If the cars have monte carlo bars I use a standard top Blaster and run the harness inside the monte carlo bar.....Cory

You have be careful with the Blaster coils..MSD wants some of them to be vertical mounted only..

[Chuck]

All oil filled coils should be mounted vertically. I go by a different wiring diagram that is actually from Ford, Cory’s came from MSD. No problem wiring up a coil with 12 volts, as long as it has the resistance built in. Stock Ford coils that I use for duraspark call for about six volts running. Rory, you could have a bad resistance wire in your harness that could be breaking down, add to that any added resistance from wiring harness connections and your ignition switch, and that’s why the car ran better. Thing of it is you’ll be okay using the six volt coil with external resistance if it’s wired tight AND you’ll be starting better when you bypass the resistor and hit the coil with full battery voltage as you crank it over. Running 12 volts I’m not sure you get that extra boost you get when you crank it over and bypass the resistor like Ford originally planned. Let me know if you need a schematic and I’ll try to post one up along with any other info I might be able to help with.

[Rory428]

Chuck, if you could post your diagram, that would be great. On my 59, they didn`t use a pink resistor wire as used on later vehicles, it has the original external ballast resistor  mounted to the firewall, that was used with its original 332 FE with points. I do have my coil, (factory Duraspark coil), mounted upright on the inner fender, even though from the factory, most of my OE Duraspark equipped late 70s Fords had the coil either horiziontal, or on an angle.
And Cory, when I looked up the MSD Blaster "2F" coil, it said that on a Ford application, a resistor was required. So now I am even more confused!

[Chuck]

Coil voltage diagram test