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In doing the DSII conversion I got a new coil, it says use with external resistor. I read that the coil must have 1.5 ohms of primary resistance to keep from burning up coil or ignition box in a v8. My new coil has 1.2 ohms resistance measured. So I have a RU4 resistor that measures 2 ohms and a RU11 that measures .5 ohms, this is not what they are supposed to be, but what I measured. Will the resistance add up with the coil and resistor (1.2 + .5 = 1.7) to give me the resistance needed?
The specs I have seen say the resistor can be 1.05 to 1.1 ohms. Not the resistance of the coil, but the inline resistor that feeds the coil. I would put the 1.2 inline to the coil and run it. You should have 9v + or - on the coil with the engine running and the coil power going through the resistor.
Forget the resistance in the coil. It's not in the equation in the books I have. You should have a duraspark II coil, the one that takes the horseshoe connector and does not have threaded pins on it. Then you need a 1.01 to 1.15 ohm resistor. The 1.2 should be close enough to work.
This will give you the best longevity of your ignition module.
I have a aftermarket Duraspark II coil it is stamped use external resistor. The coil has resistance of 1.2 by itself. So disregard this and put 1.01-1.15 resistor in line with the positive wire coming from ignition switch to the coil? There is no condenser hooked to the coil correct? I'm getting 11v at coil and 12v at battery not running, going to put dist in after I get coil figured out.
That's correct. Sometimes there is a condenser, but it's just to help get rid of noise in the radio. You won't get a good reading on the voltage unless it's running.
Do you have a starter solenoid(relay) on the pass side fender that has two small terminals or just one? It will have two large and one small, or two large and two small.
Forget the resistance in the coil. It's not in the equation in the books I have.
You generally know your stuff and that may be what the books you have say but it isn't correct. You have to add the resistance of the primary side of the coil to a resistance equation in this application.
So yes peka the 1.2 of the coil and .5 of the resistor will give you a 1.7 total and that will work.
FWIW IMO 1.2 is just fine, I do not use a resistor in my truck and use a low .45 ohm resistance coil. Primary resistance is a performance vs. component life equation. If you want a better chance of the coil and box lasting a long time have as much as 3 ohm total. With my .45 ohm total though I haven't killed a cheap box in many years. Points systems had about 3ohms for a V8, a DSII can handle less.
If you do use a resistor bypass it during starting using the 'I' post on the starter solenoid. You'll have to get a solenoid with 2 big 2 small posts for that though.
This is from the 1981 EVTM, and shows what Dave is saying - a 1.1 ohm ballast resistor is needed with the DS-II coil. Note that it is separate from the coil, so the 1.1 ohms doesn't include the resistance of the coil.
If you had the two small terminals, the one that is labeled "i" can be hooked directly to the coil +. This terminal has 12v on it during cranking only. What this does is give you a hotter spark for the short period of time during cranking by giving the coil a full 12v. You will notice this mostly during very cold weather, the engine will fire up faster. The voltage is low during this time anyway since the starter is drawing the battery down.
This is the way the older trucks wired the resistor bypass. Our trucks used a auxilary terminal in the ignition switch, so they eliminated the other small terminal on the starter solenoid.
P.S. In Gary's diagram above you can see the bypass built into the switch. If you look all the way to the right of the blue box which is the switch, you will see a br/pk wire that is hot only in the start position. This sends full voltage to the coil during cranking only. You could use this wire if you could pick it up off the switch.
is the wiring the same for 1984 ? So when it is in run, current goes thru a 1.1ohm resistance wire on its way to coil, but not in start. If I use a external resistor wired inline just before the + coil. I need another wire either coming from the switch or solenoid going to the + of coil ?
The factory resistor is actually a resistance wire buried in the harness. If you connect the R/LG wire to the coil and ground the other side you should see about 7v on the coil with the key on. That means the resistance wire is working.
I measured the voltage at the coil, with the - of the coil grounded and the + side of the horseshoe connector connected and the key in run I measured voltage across the coil and got 5.35 volts, battery at 12 volts and with horseshoe connected measuring across coil 11.35 volts. engine not running
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