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It doesn't need to be that critical. 1.5-1.8 ohms is fine. a tenth of an ohm here or there wont make a difference. You could test 100 resistors and get many slightly different readings, but they'd all work the same.
 

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"That is only if the points are closed. Points open, 12v in, 12v out."

"That most likely means it's good, just that the points are open. There is no voltage drop unless there is a load on it."

For once, excellent advice from 65 Tony, finally.

"1% tolerance? Room temperature? Is that the factory specs? Right or wrong I'd like to see those specs!"

All one has to do is look at the Delco-Remy specs given in the manuals, that is what the factory uses, NOT yours.

"How many people on this site do you think have a ohm meter that reads accurately to .018 ohms or even within 50% of 1.8 ohms.
I prefer testing voltage under operating conditions instead of using a ohmmeter."

The real question is, how many people actually know how to use, read and get accurate results from their meters? Obviously, you didn't further their knowledge of how it really works, which troubles those people that do know how to read one properly.

Most digital, and some later analog meters use some part of an ohm to work with. We routinely see values that were higher than specified, so, when we read, we first cross the meter leads, and gt the meter use ohms, THEN, read the part. Example, we see a given value of 1.602 ohms, with a meter use read of 1.02 ohms, the part is a 1.50 ohm read.

We in the shop all agree completely with you, Don, voltage load is essential, far more than ohms readings, but, there is no way to read a part for voltage output vs load in an auto parts store, when you are buying a replacement part, so, ohms it is.

Willard Thompson
 

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Trifive Automotive Electrical Wiring Expert
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" Obviously, you didn't further their knowledge of how it really works, which troubles those people that do know how to read one properly."
Sorry I troubled you.
"Most digital, and some later analog meters use some part of an ohm to work with. We routinely see values that were higher than specified, so, when we read, we first cross the meter leads, and gt the meter use ohms, THEN, read the part. Example, we see a given value of 1.602 ohms, with a meter use read of 1.02 ohms, the part is a 1.50 ohm read."

Thanks for explaining that with the new math.
 

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Oh, it isn't "new math" it is the same cenuries old math that actually works. Has for us all along. It worked for Mickey, works for me, works for everybody I know that knows how to do it, enough said.

Willard Thompson
 

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"That is only if the points are closed. Points open, 12v in, 12v out."

"That most likely means it's good, just that the points are open. There is no voltage drop unless there is a load on it."

For once, excellent advice from 65 Tony, finally.

"1% tolerance? Room temperature? Is that the factory specs? Right or wrong I'd like to see those specs!"

All one has to do is look at the Delco-Remy specs given in the manuals, that is what the factory uses, NOT yours.
Willard Thompson
But I didn't give any specs. ?
Are the coils you use measured to the same 1% tolerance?
 

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It doesn't need to be that critical. 1.5-1.8 ohms is fine. a tenth of an ohm here or there wont make a difference. You could test 100 resistors and get many slightly different readings, but they'd all work the same.
That is correct. In fact I see new ones that say "2 ohms" in the specs. It's simply a mystery how these cars run smoothly at all!
 

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PROPER resistance is done with one wire disconnected, and the meter leads across the resistor, and THE CORRECT READING AT ROOM TEMP SHOULD BE 1.80 OHMS, +/- 1 PERCENT.
So if 1% was it's tolerance, then I suppose all the wiring involved had to be within 1%. The resistance between the negative battery post, to the points, through the coil, to the resistor, through more wiring, through the ignition switch, and back to the positive post on the battery would have had to be within 1% or the ignition wouldn't work properly. 1% of what, I don't know. Certainly it wasn't 1.8 ohms. And the operating voltage of the generator/voltage regulator would have to have been within 1%, or the tight tolerance of the coil would have been an absolute waste. What was the resistance of all that wiring in the service manual? What is the rated output voltage tolerance of the charging system?

Wow! o_O It really is a mystery these cars ever ran at all! :ROFLMAO:

And all these trifives with newer wiring using heavier gauge wire... I suppose they are just burning up points and coils like there is no tomorrow.
 

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How many people on this site do you think have a ohm meter that reads accurately to .018 ohms or even within 50% of 1.8 ohms.
I prefer testing voltage under operating conditions instead of using a ohmmeter.

See post #5.
Not arguing with you, just saying that my "good" meter only goes down to the tenth ohm. I do have another one that does go down to the thousandth's, but would never bother using it to check a ballast resistor. I think the highest resistance it measures is 99 ohms.
 

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PROPER resistance is done with one wire disconnected, and the meter leads across the resistor, and THE CORRECT READING AT ROOM TEMP SHOULD BE 1.80 OHMS, +/- 1 PERCENT.
So like later stated, you need to measure voltage and do the math, I suppose you have to make that reading within maybe one second or less or the ballast resistor would almost instantly be above room temperature and throw off all your math?

If it actually says 1% in the manual, the engineers were off their rockers. I don't have a manual, could you possibly show a pic of those specs? Or at least tell us what page it's on in what manual.
 

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Trifive Automotive Electrical Wiring Expert
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first cross the meter leads, and gt the meter use ohms, THEN, read the part. Example, we see a given value of 1.602 ohms, with a meter use read of 1.02 ohms, the part is a 1.50 ohm read.
..............................
Oh, it isn't "new math" it is the same cenuries old math that actually works. Has for us all along. It worked for Mickey, works for me, works for everybody I know that knows how to do it, enough said.

Willard Thompson
The old math confuses me. 1.602 minus 1.02 = 1.50
 

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I thought I'd make a couple of comments having been down this road recently;
It is my experience that ballast resistance values don't change much from hot to cold, maybe 10% but probably less.
Your car's voltage can vary from as low as 12.0V when not running to over 14.0V when running. That is ~15%.
Ballast resistor's resistance will vary. I recently bought one with 0.4 Ohms of resistance and another with 1.8 Ohms. The 0.4 Ohm ballast resistor was used in 1960 and 1961 high performance SBC with dual points - I believe.
Before about 1955 cars with 6V systems did not use ballast resistors. Ballast resistors are used on 12V systems presumably to lower the current the points see and extend their life.
Somewhere in the 1960's GM started using resistor wire on some cars in lieu of a ballast resistor from the firewall electrical plug to the coil. This effectively accomplishing the duties of a ballast resistor.
Hand held ohmmeters don't read low values (under 1.0 Ohm) of resistance very well. If interested I can explain why.
Al
 

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Oh, it isn't "new math" it is the same cenuries old math that actually works. Has for us all along. It worked for Mickey, works for me, works for everybody I know that knows how to do it, enough said.

Willard Thompson
I don't know? I get .582 ohms
 

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Hand held ohmmeters don't read low values (under 1.0 Ohm) of resistance very well. If interested I can explain why.
Al
I have a hand held ohm meter that reads as low as .001 ohms. Granted most people don't have one of those. As for the test lead resistance, you simply clip them together then hit the button to zero the meter.
 

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I've bought and used ceramic ballast resistors for Chevy, Ford, and Chrysler, and used them all in my Chevys. It's just not that critical, or nearly the accuracy that some people seem to be worried about. You just need to reduce voltage across the points to keep from burning them up. Or for some electronic points conversions to keep from burning those up also. My Accel electronic conversion requires a ballast resistor ahead of it to work, and protect the unit also. I've got a Chrysler resistor ahead of it, but didn't tell my coupe what it was.
 

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A tenth of an ohm through an ignition resistor does not mean jack an ignition resistors job is to kill some voltage through the points when they ground to extend point life. A variance of resistor output voltage may / may not change the points / condenser service interval by an inordinate number of plus / minus miles.
In the meantime the trade off of extending point life by reducing voltage is that your ignition coil is now operating @ less than 8 volts = weak spark to the plugs. If the engine continues to run after starting the resistor has continuity = in / out is connected. Next, to determine if it is functioning: Touch the resistor if its hot it is working.
 

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Yes indeed! Leave your key turned on with the points in the right position, and you'll get the resistor hot enough to burn paint on your firewall! Don't ask how I know! :)
I got one hell of a 2nd degree burn off mine some 40+ years ago from leaving the key on and not just touching, but grabbing it so I could screw it back into the firewall. Never again! I forget a LOT of things, but that one is Burnt into my memory. The paint deal just plain sucks. You should put a layer of asbestos behind it! 😉
 

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Better to just not leave the key on, or disconnect the wire to the coil if you do. No load, and it wont ever get hot. Better yet put a switch ahead of the resistor in a hidden location to defeat it. It will save heating issues and add another level of security to the car.
 

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Another function of the ballast resistor is to allow better spark when cranking.
The ballast resistor, coil and points are designed to provide adequate spark when the engine is running normally, with the expected 12.6 to 14.4 volts.
When cranking, the system voltage drops, sometimes as low as 9.6 volts with a reasonable battery and a properly working starter.
The ballast resistor is bypassed during cranking to apply the reduced voltage directly to the coil, so that a pretty much normal spark intensity can be delivered to the spark plugs.

I wouldn't trust a handheld ohm or volt meter to be accurate to 1%. I do rely on my Home Depot $30 VOMs to be within 10% or so.

The reason older ballast resistors are encased in ceramic and wire wound instead of carbon is to survive and continue to function properly when they get hot from use.
I suppose resistance wire can replace a separate ballast resistor, because the waste heat is distributed over the full length of the resistance wire.
So the wiring harness is then only 'slightly' warmed up? IIRC, the insulation covering the resistance wire is made of a different material to withstand higher temperatures.
 

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A tenth of an ohm through an ignition resistor does not mean jack an ignition resistors job is to kill some voltage through the points when they ground to extend point life.
It's worse than that. He is saying that anything over/under 100th of an ohm off the mark is not acceptable. But he, or they are the experts. Hmm?
 
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