Duraspark conversion, coils, and pink resistor wire

[66 E100 Pickup]

Hi all, I am proceeding with my duraspark conversion on my '69 200 six.

I have read the stickies several times, but I need to revisit the issue of voltage supply to the "+" side of the coil as there seemed to be a lose end on the issue.

Let me recap according to my understanding:

1) the stock duraspark ignition coil, as connected correctly, gets a full 12 volts during cranking, and 6-7 volts during normal run mode;
2) the full 12 volts will retard the timing to allow for easier engine cranking;
3) 6-7 volts will keep the ignition coil from overheating and shortening it's life expectancy;
4) The 6-7 volts is achieved by bringing in a 12 volt line upstream of the fat pink resistor wire (some 60" long) that connects near the ignition switch

Now my question--is anybody running 12 volts continually to the stock coil, with what results? What about 12 volts continually to a perfomance aftermarket coil such as a Jacobs, etc., anyone run into issues?

Does the 12 volt vs 6-7 volts have any effect on the module life expectancy?

Thanks,

John

 

[CoupeBoy]

I've got a duraspark distributor but using GM HEI ignition module. I used the factory coil wire to trip a relay that feeds 12v to both the HEI module and the factory coil. No problems yet, but I know I should be using a 12v coil instead of the factory one, I'm sure it's just a matter of time before 'she blows'.

-ron

 

[fb71]

do not run the stock coil on straight 12v. It will overheat and fail relatively quickly. The stock coil gets straight battery voltage during cranking because battery voltage can drop to 9v during cranking. Running it thru the resistor would result in 4-5v at the coil, which is not sufficient. An afternarket coil like an MSD Blaster or Pertronics Flamethrower is needed to run at 12v, or a stock TFI coil from a fuel injected 80's or 90's Ford. The stock Duraspark module can easily handle an aftermarket coil at 12v.

 

[CoupeBoy]

FWIW, my stock, going to die original (non-12v) coil has been in there and wired to 12v since 2000. However I have maybe 7000 miles on the carsince then, including round trip from Ft Collins, CO to Bismark, ND in one day, otherwise mostly short trips under an hour. Not saying this is anything that anybody should reproduce but it most likely won't fail right away, it will wait, biding its time then one day when I'm 100 miles from nowhere it's going to fry on me and leave me stranded. Just because it works is no reason to rely on it. For me it's all part of the adventure.. will I make it home today?

-ron

 

[Anonymous]

I'm running the full 12v to a Pertronix Flamethrower coil. No problems so far (been about a month / 500 miles). I used a relay in a similar manner to CoupeBoy (but I'm feeding a Duraspark ICM as opposed to a GM HEI).

As I understand the Duraspark ICM, it's not the full 12v that retards the timing during start, it's the white wire from the module... it needs to be fed by a 12v source that is switched on only during starting (someone please correct me if this is wrong).

 

[fb71]

As I understand the Duraspark ICM, it's not the full 12v that retards the timing during start, it's the white wire from the module... it needs to be fed by a 12v source that is switched on only during starting (someone please correct me if this is wrong).

dead-on. Be aware, not all DS modules have a white wire. If it does, it can be connected to the 'S' terminal of the starter "solenoid" (see another post) to retard timing for easier starting.

 

[66 E100 Pickup]

Ok everyone thanks for the help.

White wire from module goes to "S" on starter relay. That's clear.

Red wire from module goes to a switched 12 volt source.

If it's a stock coil, it *should* be fed 6-7 volts via the pink resistor.

Otherwise, give it the full enchilada of 12 volts. Would it be safe to say that both the red wire from the module, and the coil 12 volt wire, can be conveniently hooked up to the "I" terminal on the starter relay?

John

 

[Anonymous]

Would it be safe to say that both the red wire from the module, and the coil 12 volt wire, can be conveniently hooked up to the "I" terminal on the starter relay?

In all of the reading/research I did on wiring a DSII, I don't recall a setup where the coil and module were driven by the "I" terminal on the solenoid. That doesn't mean it's not possible, I just haven't read anything about it... so don't take my word for it.

If your goal is to get 12v switched to the coil and ICM WITHOUT tapping into the dash harness, you can do what I did:

 

[Lazy JW]

According to the schematics in my manual, Ford used the resistor wire in the early DS2 ignitions, then deleted it in the later models. My 81 F-150 doesn't have a resistor, nor does the solenoid have the "I" terminal. They appear to all secify the same coil.
Joe

 

[66 E100 Pickup]

If your goal is to get 12v switched to the coil and ICM WITHOUT tapping into the dash harness, you can do what I did

:

Bengoshi, where does/did that 16 ga Red/Green stripe wire go to originally? Did you pickup one of those ice cube style relays at an electronics store for your relay?

Joe, do you get 12 volts at your coil? I wonder if Ford decided to put in a "hotter" coil for later gen DSII's?

Thanks guys I am now finally getting my arms around this. I have not yet verified that I DO have that fat pink wire in my '66 loom. I have both a stock horsehoe connector coil, and a Jacobs Ultra Coil, that I can use. I would prefer the stock look but I think this engine will do better with a bigger spark (it's got a tendency to foul up two of the plugs).

John

 

[Anonymous]

Bengoshi, where does/did that 16 ga Red/Green stripe wire go to originally? Did you pickup one of those ice cube style relays at an electronics store for your relay?

The Red/green wire in the diagram originally went to the + side of the coil... it's the same wire that's downstream from the pink resistor wire. (the #16 comes from the number assigned to it on a 1966 mustang wiring diagram that I have laying around somewheres...)

The relay is a standard automotive 30 amp type readily available at any auto parts store or radio shack.

 

[fb71]

All cars/trucks originally equipped with points have the resistor wire. Early DS cars (1974) had the resistor and used the points coil. DS II cars do not use the resistor, and use a DS-specific coil. (according to an FMC technical suppliment dated 1983)

 

[66 E100 Pickup]

The Red/green wire in the diagram originally went to the + side of the coil... it's the same wire that's downstream from the pink resistor wire. (the #16 comes from the number assigned to it on a 1966 mustang wiring diagram that I have laying around somewheres...)

Ok I see now. I guess you haven't had any trouble closing the 12 volt relay with only 6-7 volts? Or, the amp requirement for the relay coil is so low that the resistor wire essentially supplies 12 volts?

I see how you have added protection to your system, I like it.

Thanks again for your help.

John

 

[bigcatchdaniel555]

my car may have had a resistor wire when it was new but i'm not sure but it definetly doesnt have one the coil on it is not a high voltage coil just a oem from advance but it dos say 12v no resistor required and thats exactly how ive run it for a year with no problems.

 

[fb71]

Ok I see now. I guess you haven't had any trouble closing the 12 volt relay with only 6-7 volts? Or, the amp requirement for the relay coil is so low that the resistor wire essentially supplies 12 volts?

OK, the resistor wire is about 1ohm. The primary side (low voltage) of an ignition coil for points is just under 3ohms. The coil is three times the value of the wire, so it gets 2/3 of the available voltage, and the wire gets 1/3. Available voltage, engine running, is just over 13v. So, the coil would get 7.5v, and the wire would get about 5.5v.

Now, replace the coil with a relay... The relay magnetic coil is about 60ohms, and the wire is still about 1. Divide 13 by 60; its 0.217. Which means the resistor wire would get 0.217v (less than 1/4 of 1 volt), and the relay coil would get about 12.78, if charging system voltage is 13v.

 

[66 E100 Pickup]

ok great! thanks for laying out the numbers. My big fat pink wire is supplying 12 volts no load. That small relay coil won't hardly pull any load so I can expect it will close just fine.

It's really quite neat how they laid this system out to reduce the voltage. But I can't wait for a big fat spark from the bigger coil.

It is tempting to stab that pig tail up at the ignition with a regular 14 or 12 gauge wire and just go direct to the coil. That's one less part to go wrong, not putting in the relay. Probably need to fuse it just in case the coil shorts out. Hmmm.

John