so I sold my '79 ford pickup recently and the buyer is paying me to throw my old tired 429 in it and get it running for him. I have everything done now except for the ignition and I have a ford duraspark2 setup, the only problem is this truck was MSD for years and I must have cut those old connections out along time ago. I found plenty of good wiring diagrams and im confident I can wire it up, I am only lacking the .8-1.6 ballast resistor they all call for.
here is my question, will a .4-.9 ballast resistor do the job since I happen to have one lying around? or will it just give me more headaches?
It will be fine. The ballast resistor is there so that when the ignition is on and the points are closed that there is a little load on the circuit besides just the coil. If the coil has enough primary resistance, you can get by without one at all. It is, of course, never a good idea to leave the ignition "on" and the motor not running with a points ignition system.
that is good to know. is it only needed on points then? because the distributor I have is hall effect. everything I have read on the duraspark setup uses hall and still calls for the ballast which was a little confusing to me. when my MSD died on my bronco I just wired up the pro billit straight to the coil and solenoid, which I thought about doing here aswell, just couldn't find any good info on it like I did with the MSD
Well, without points, what you have is a transistor that acts like a set of points, that is, a simple switch. They may want the ballast resistor in there to limit current flowing through the transistor. The circuit is still the same (not with the MSD or a capacitive discharge type, which works different.) My recommendation is still the same, and the difference in resistances of the 2 resistors should not effect your transistor switch, but I would put it in the circuit. Transistors are a lot less "robust" electrically than points. Overheat them once or flow too much current once and they are shot. If you are really, really were concerned, you could put 2 of your 0.4-0.9's in series and come up with the 0.8-1.6 (1.8 in this case) resistor. Remember that the coil is in series too, and coil resistance can vary that much. With a transistor switch, I would make sure to use the proper coil (primary resistance) for that circuit.
I was under the impression most transistorized ignition setups only power the coil then they get a pickup signal, making a ballast unneeded.
ok thanks for giving me a little more insight into this. I admit I don't know as much about ignition as I ought to by now. but you just answered many questions I had in a matter of two posts and I appreciate that very much. the coil, distributor and ignition box are all factory ford parts of the same era and have worked as a team before on my bronco so im fairly confident they will work together again just fine, the only new element is the Datsun ballast. thanks again!
Kenny, "it depends." A Megasquirt setup is virtually identical to a points system: Battery - ignition switch - coil primary - megasquirt "coil driver" IC, which is really just a high current switch, ground. That particular one can handle the load without a ballast resistor in series with it. The one 2K4Kcsq is dealing with replaces the megasquirt circuit with a Ford box that would like to see a ballast resistor in series, apparently. The circuit works on flyback, invented by Tesla (the man, not the car company,) BTW. The coil is not a coil but 2 coils together, AKA, a transformer. With the points (transistor) closed, current flows through the coil building up lines of magnetism around the primary and intersecting the secondary coil. The lines/field is not moving and the coil is now "charged." Voltage/current is induced in the secondary when the lines cut through the secondary coil, not when the lines are stationary. When the circuit opens from the points on the cam or the transistor turning off from the computer, the lines collapse, cutting through the secondary coil as they get smaller/colapse and inducing the output voltage spike that jumps across the spark plug.
Now, other electronic ignition systems like MSD are a "capacitive discharge" type and they don't charge the coil like that. Instead, they work more like a conventional transformer and shoot a big pulse through the primary when the secondary is supposed to fire. They have the primary side of the coil not wired to 12V at all, but to the transistor containing box.
If you're using a Duraspark ignition with the OEM type Ign. module then you do need a ballast resistor to protect the box from frying. It is only to get a full 12 volts on starting and then something less after the engine is running by having the power go through the ballast resistor.
Not to steal the thread, but . . . my ACCEL distributor and coil set-up calls for this one:
http://www.ebay.com/itm/200720326535?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
Is this specific resister really necessary or will any one from my local FLAPS work as well?
Kinda ties in with the initial posters question to a degree.
Thanks,
TC
update: I wired everything up and I do have a nice spark so I must have done something right 
now to sort out my fuel issues and hopefully send this thing down the road soon. my first vehicle will be missed but not as much as the rest of my projects I have been waiting to work on the last few years. if I had an acre of property I would just keep them all 
TeamEvil: I figured you would be interested in the update since the ballast I used was only half the resistance called for and it still seems to work. I would just find one close and give it a shot like Dr. Hess said.
