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Ballast resistor question

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flyrc100

New member
First time post here, so here goes:

I got an 1988 5.0 (305 chevy) with a coil/alternator ballast resistor I managed to mangle. The ignition is a stock points Prestolite Marine distributer. From reading up on voltage drop and all that good stuff, it seems I should get a 0.7ohm replacement, (Figuring dropping the voltage from 12 to 8 volts or so also maybe 4 or 5 amps to power the coil) , but resistor in question actually read 70 ohms on a meter. Wondering how I could be so far off on a fairly simple calculation?

Or maybe there is a sight were I could locate the exact replacement part? Thanks
 
Is the meter you have accurate for reading a resistance that low...?? maybe the increased resistance is due to the "mangle"? If you are talking about the ignition ballast resistor most are in the 1 ohm range. Its sole purpose is to limit the current flow and its resistance will change with temperature.
 
makomark said:
Is the meter you have accurate for reading a resistance that low...?? maybe the increased resistance is due to the "mangle"? If you are talking about the ignition ballast resistor most are in the 1 ohm range. Its sole purpose is to limit the current flow and its resistance will change with temperature.
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Unknown how accurate the meter is. Its a mid priced Sears Craftsman. I really do not know if 70 ohms is a "low" reading. The resistor itself was in a rubber housing, I cut I out and it reads 68ohms +/- 10% 5 watts, actually printed on the side. Again, I'm having a hard time believing that value, I agree with you something under 1 ohm seems to make the most sense. I might just work backwards, buy a resistor and check the coil voltage on the running engine. If its round 8 or 9 volts, I will have sized the thing correctly.
 
If it is printed with 68 ohms, then there's nothing wrong with it...other than being disconnected....I'd be willing to bet it isn't your ballast resistor....BTW, I've never seen a ballast resistor encased in a rubber housing...they get hot and the rubber wouldn't last long.
 
kimcrwbr1 said:
Hook the resistor to the coil and key on hot then measure the voltage at the coil with the key on. If your getting 8-9 volts you should be just fine. The reason for a ballast is to keep the points from cooking.
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Yes I got 8-9 volts with he engine running. I actually bought a 68 ohm resistor online that looks most identical to the one I Mangled. I checked the new one against the mangled one and my meter checked them both to be right at 70 ohms. So now Im feeling pretty good that the meter is accurate and I am in fact dealing with 68 ohm resistor, not a 0.7 ohm.

The new resistor simply has better leads. I made a new wiring harness with it and put it on the alternator. It goes on the purple wire terminal, so I guess it must be for the coil. Anyway the engine popped off in the driveway. Ill take it to the lake this weekend to confirm voltage and all that good stuff. It took awhile to convince myself it was a 68 ohm resistor, but it does in fact appear to be the case.
 
If it is up at the alternator, it's not likely to be a ballast resistor for the ignition system....it's more likely to be a current limiter for the excitation circuit in the alternator....
 
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