rexus31
Senior Member
With the key in the On position, should I be getting 12V to the Ignition Side of the Ballast Resistor?
Voltage Question - 1965 Chrysler 300
- Thread starter rexus31
- Start date
If by "ignition side", you mean the side that goes to the ignition switch, then yes. On the coil side, the voltage will depend on the resistance value of the ballast resistor.
rexus31
Senior Member
Thanks John. I had a poor connection on the Ballast Resistor that was causing all kinds of problems. Problem fixed.
A simple and accurate test for this is a voltage drop. Put one voltmeter lead on the battery turn on the circuit and put the other voltmeter lead on the wire into the ballast. Your volt reading indicates how much resistance the circuit has... it should be less than .5v and by the time you lose an entire volt the circuit cant work correctly.
You already know the ballast has resistance. To test from the ballast to the coil...same idea one lead at the ballast out and the other lead at the coil +. Same as before .5v or less is a generic spec. less is better for wiring resistance.
When you test a circuit under its operating load, you get a real idea of how its working... cant do that with ohms.
You already know the ballast has resistance. To test from the ballast to the coil...same idea one lead at the ballast out and the other lead at the coil +. Same as before .5v or less is a generic spec. less is better for wiring resistance.
When you test a circuit under its operating load, you get a real idea of how its working... cant do that with ohms.
rags
Senior Member
to test this circuit under load, his points would have to be closed? with electronic ign. he would have to ground the coil? good technical point about voltage drops. it's something not many people understand.
Sorry... my mistake... yes. I had the thought in my head of doing the test while running or cranking. Amazes me how hard it can be to get information simply and accurately across this way... I'm accustomed to being there and speaking instructions, usually one at a time while checking that its done right from time to time.
rags
Senior Member
actually would it be done key on engine off? if done while running, the load would occur as a function of dwell time and i think would show lower than correct voltage drop. agree, diag'ing from a distance is a real b!tch. good exchange though.
I personally, would crank the engine... or running if possible. You are correct about the dwell issue, but initial VD test would just be for quick verification... small mv, keep moving... closer to the .5 spec(.2,.3), probably ok... anything else is a definite issue (if not the root cause). I would let it sit on closed points to verify anything questionable to be sure, but why do that if there was no cause indicated.
BTW, I am big on just cleaning up anything I can do quickly... no need to charge extra when you're in a diagnostic fee and lets you look at connectors pins. Careful with electronic ignition, some will discharge a single spark when the key cycles off... and I couldn't tell you which ones (hall effect pick up on a guess).
Yes I enjoy comparing notes with someone who speaks the language... And you made me have to think too... bonus.
To relate all this back to the issue rexus31 was enjoying... The voltage drop test most likely would have shown the resistance on that circuit and then closer inspection and terminal cleaning would have proved it to be at that connector... Another voltage drop to verify that circuit is solved... on to the next problem.
rags
Senior Member
ditto to all above. i would have done it with constant load especially using a digital volt meter and looking for small voltages throughout a circuit. just too many variables otherwise. fewer things going on electrically the better for the test. do hope his problem is finally resolved.
I don't disagree, but I have an aversion to shorting the points without a compelling reason. Most DMMs I have owned have the bar graph at the bottom of the display that is useful sometimes to at least see pulsing voltage. Long ago, I was convinced to purchase a fluke 88, which has a graphing feature I used once or twice... Now I wonder if that feature would have helped on this test. KOEO would be like 50/50 shot for closed points and could work too, but I cant see a way to trust the results.
rexus31 has dealt with this long enough. It would be nice if this is the end of the problems.
rexus31
Senior Member
Just for clarification, I'm running a Pertronix Ignitor module and coil. The Ballast Resistor isn't a resistor at all in my case. I removed the guts and soldered a wire in place to allow full voltage to the coil to power the Pertronix module while retaining the stock appearance.
rags
Senior Member
good clarification. that meter with a graphing feature is a good choice for this type of test and would lead to a correct diagnosis. oops, in fact, no ballast resistor! doh! thanks for a good discussion, SG
Similar threads
