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Discussion Starter #1
ok- have 69, with resistance wire, points ignition.
externally regulated.

voltage readings on coil + as follows:

ign on= 7.5 volts
motor running= 12.5-13 volts

i thought the purpose of the R wire was to reduce voltage during run so points didn't burn out.

does the motor need to run and get the R wire warm before it will drop the voltage?

other possibility is the yellow wire to starter is staying hot during run. but sems unlikely, as v is 7.5 volts with car off and key to run.

any suggestions, idea, comments?

thanks

toph
sd,ca
 

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will likely be the solenoid is bad if your still reading 12v when running. should only be the 6 -7.5v after the resitor wire at the + terminal when the engine is running and no more.. start it up and pull the yellow lead and see if its still got power. If it does, pull the solenoid and replace it. You will surely burn your points.
 

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Discussion Starter #3
thanks for the reply.

ok- disconnected yellow wire from sol to + coil- zero voltage. solenoid ok. hmm.

still 12.5 just from resistance wire (white cloth with yellow tracer). can start car without sol hooked up.

strangely sometimes, with key in on position, the voltage at the coil is 7.5V, but most of the time it's 12.5. always 12.5 when running.

what could be going on here? how can the wire sometimes act as a resistor and sometimes not?

any suggestions?

thanks

toph
sd,ca
 

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check to see if its jumped or shorting. Cant think of a reason for multiple voltages other than that. should be one wire to R and one from there to coil no more.
 

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Discussion Starter #6
ok Bob, you got it right. i saw your old post and was about to do this.

made sense- just had to prove it to myself- and sure enough-

ignition switch on, + v-meter on coil, - v-meter lead to ground:

points open with matchbook between contacts= 12.5V

points closed after removing matchbook= 7.5V

there you have it.

so- reading the voltage off of the resistance wire going to coil is not a valid test for ignition/points voltage.

in addition- the voltage to coil changes so fast when the car is running (due to opening and closing of points) that my V meter was staying high all the time. ie., no fluctuation.

thanks for the post-

toph
sd,ca
 

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Sounds like this one is figured out. The signal on the positive size of the coil will be roughly a square wave that alternates between about 8 volts and 12 volts. It depends on the system voltage (which usually is 13 volts or more under charge). But anyway, we can assume about a 4 volt span.

The square wave signal has a duty cycle equal to the dwell reading or about 30%. So the value measured by a DC volt meter will be about 70% of this 4 volt span below the system voltage. 70% of 4 is about 2.8 volts. So if the charging system is holding the system voltage at 13.8 volts, the coil will show 11 volts on the coil + terminal as measured by a DC volt meter. In reality though, 13.8 is conservative for system voltage which can go as high as 14.5 volts or higher.

The main thing the resistor does is limit current flow. The voltage reading is an artifact of the current limiting effects. Looking at it another way, the resistor gets hot and essentially is disipating heat that would otherwise be disipated by the ignition coil itself. The coil gets pretty warm on it's own, but without the resistor it would get even hotter.

If you ever encounter someone complaining of intermittant ignition problems and see that the top insulator of the coil is cracked or the bottom is pooched out, you're probably looking at a coil that has over heated. More than likely this is because the ballast wire / resistor has been bypassed in a breaker point ignition system or electronic system which requires a current limiting resistance.
 
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