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I recently did the duraspark 2 swap into my 85 f150 but I haven't put in a ballast resistor yet. I drove it a couple of weeks until it started eating modules. My first question is would not having a ballast resistor on the wire to the coil cause the modules to go out? I figured if anything the coil would go bad, and I had a spare so I wasn't real worried about it. My local auto parts stores don't have and cant get a resistor for a few days, so I'm hoping Radio Shack can help. Anyone able to tell me the specs on the resistor I'll need? Thanks guys.
Slifer, you're right, the ballast resistor limits the current flow through the coil. It also limits current flow through the module by way of the negative coil wire, so I suspect the extra current was heating up the modules and causing the failures.
The value for the resistor is about 1.2 - 1.3 ohms. Early Chryslers and 50's Chevrolets used them, and Jeep uses them on their fuel pump circuits. If you get one from Radio Shack as a temporary replacement, make sure you isolate it from any painted surface, because they get very hot.
The module would have to switch extra current without the resistor. I don't have the spec in front of me but I think it is 1.2- 1.5 ohms. Mopar used a ceramic cased one that would work. A real electronics supply can get you one. I would get at least a 30 watt one.