C3 Tech/Performance V8 Technical Info, Internal Engine, External Engine, Basic Tech and Maintenance for the C3 Corvette
Sponsored by:
Sponsored by:

1972 350 coil wiring ....?

Thread Tools
 
Search this Thread
 
Old 09-09-2015, 04:38 PM
  #1  
Wee
Drifting
Thread Starter
 
Wee's Avatar
 
Member Since: Apr 2010
Location: Cartersville GA
Posts: 1,857
Received 333 Likes on 237 Posts

Default 1972 350 coil wiring ....?

Shouldn't the red wire also be hooked up to the positive terminal...?




Brian
Old 09-09-2015, 05:20 PM
  #2  
ddawson
Le Mans Master
 
ddawson's Avatar
 
Member Since: Mar 2001
Location: Lincoln, CA
Posts: 5,649
Received 598 Likes on 485 Posts

Default

Do still still have points? Could be the resistor wire if not.
Old 09-09-2015, 08:49 PM
  #3  
LT-1 kid
Melting Slicks
 
LT-1 kid's Avatar
 
Member Since: Sep 2007
Location: cary Il
Posts: 2,096
Received 244 Likes on 169 Posts

Default

if you have points it would not matter, I like to put the red wire on the +
Old 09-09-2015, 10:02 PM
  #4  
Wee
Drifting
Thread Starter
 
Wee's Avatar
 
Member Since: Apr 2010
Location: Cartersville GA
Posts: 1,857
Received 333 Likes on 237 Posts

Default

Looks like points to me...But it's been over 30 years since I worked on anything with a set of points. Cap, rotor button and points are new, installed by the previous owner. They seem to be in great condition. I don't think this wire has anything to do with my problem of dieing at a stop light....That story can be read here...













Brian
Old 09-10-2015, 09:09 AM
  #5  
jnb5101
Le Mans Master
 
jnb5101's Avatar
 
Member Since: Jul 2006
Location: charlotte north carolina
Posts: 8,117
Likes: 0
Received 100 Likes on 92 Posts

Default

Remember that there are two power sources for the coil. A "full" 12 v source for when the engine is cranking (reduced somewhat by the load from the starter), and a resistor wire that reduces the coil supply voltage to about 10.5 volts. This reduced voltage is what the coil is designed to operate at when the engine is running. Supplying 12v to the coil continuously will over heat the coil and burn the points. It appears that only one wire is connected to the coil. Test the voltage on the + terminal of the coil with the motor running-it should be less than 11v. Also test the red wire with the ignition switch in the "start" and "run" position.
Old 09-10-2015, 03:50 PM
  #6  
dan1495
Burning Brakes
 
dan1495's Avatar
 
Member Since: Jan 2006
Location: Clear Lake Shores Texas
Posts: 987
Received 263 Likes on 184 Posts
2016 C3 of Year Finalist

Default

I agree with JNB. If a car has points and a ballast resitor is not utilized in one form or abother the car will run well for about 50-100 miles at which point the points can burn and the car will quit running. Ask me how I know..
Old 09-10-2015, 08:22 PM
  #7  
Big2Bird
Le Mans Master
 
Big2Bird's Avatar
 
Member Since: Dec 2006
Posts: 8,823
Received 1,014 Likes on 808 Posts

Default

Originally Posted by jnb5101
Remember that there are two power sources for the coil. A "full" 12 v source for when the engine is cranking (reduced somewhat by the load from the starter), and a resistor wire that reduces the coil supply voltage to about 10.5 volts. This reduced voltage is what the coil is designed to operate at when the engine is running. Supplying 12v to the coil continuously will over heat the coil and burn the points. It appears that only one wire is connected to the coil. Test the voltage on the + terminal of the coil with the motor running-it should be less than 11v. Also test the red wire with the ignition switch in the "start" and "run" position.
The purpose of the ballast wire is to limit the circuit current to 4.4ampers.
Voltage has nothing to do with it.
Not trying to be an azz, just trying to clarify how it works.
The following users liked this post:
69427 (09-10-2015)
Old 09-10-2015, 09:47 PM
  #8  
69427
Tech Contributor
 
69427's Avatar
 
Member Since: Jun 2004
Location: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Posts: 18,346
Received 767 Likes on 549 Posts

Default

Originally Posted by Big2Bird
The purpose of the ballast wire is to limit the circuit current to 4.4ampers.
Voltage has nothing to do with it.
Not trying to be an azz, just trying to clarify how it works.



(If only someone would write up a sticky explaining all this stuff.)
Old 09-10-2015, 10:05 PM
  #9  
Big2Bird
Le Mans Master
 
Big2Bird's Avatar
 
Member Since: Dec 2006
Posts: 8,823
Received 1,014 Likes on 808 Posts

Default

Originally Posted by 69427



(If only someone would write up a sticky explaining all this stuff.)
(If only)

Hi Mike. Long time.
Old 09-10-2015, 10:06 PM
  #10  
Wee
Drifting
Thread Starter
 
Wee's Avatar
 
Member Since: Apr 2010
Location: Cartersville GA
Posts: 1,857
Received 333 Likes on 237 Posts

Default

Is it safe to say that the black wire (as pictured above) has to be wired to be hot with the switch in the run position and not just when the switch is in the crank position.....Otherwise the car would start but then just go dead....?

The red wire that is not hooked up is made of 8 or so strands of very stiff wire, silver in color. It had a cloth covering most of which is gone but can be seen where enters the rest of the harness, I'm pretty sure it's the wire that is supposed to be hot when the key is in the run position.

So it looks like I have wiring issues to figure out....The battery isn't hooked up so I didn't get a chance to check if the red wire has any power at all.

Brian

OK looks like I need to go read the sticky....I did read an old post between Roger and 69427 about these issues....But it was over my head.

Last edited by Wee; 09-10-2015 at 10:14 PM.
Old 09-10-2015, 10:17 PM
  #11  
Big2Bird
Le Mans Master
 
Big2Bird's Avatar
 
Member Since: Dec 2006
Posts: 8,823
Received 1,014 Likes on 808 Posts

Default

Originally Posted by Wee
Is it safe to say that the black wire (as pictured above) has to be wired to be hot with the switch in the run position and not just when the switch is in the crank position.....Otherwise the car would start but then just go dead....?

The red wire that is not hooked up is made of 8 or so strands of very stiff wire, silver in color. It had a cloth covering most of which is gone but can be seen where enters the rest of the harness, I'm pretty sure it's the wire that is supposed to be hot when the key is in the run position.

So it looks like I have wiring issues to figure out....The battery isn't hooked up so I didn't get a chance to check if the red wire has any power at all.

Brian
Nothing is safe to say without testing.(You just don't know what someone else has done).
One wire "should" go to the R terminal of the starter. It gives full voltage/current while cranking only.
Another wire "should" be keyed on while in run, and should have a resistance wire in series with it to limit the ignition primary current.
If you have a VOM and know how to use it, now is the time to check.
Old 09-10-2015, 10:28 PM
  #12  
69427
Tech Contributor
 
69427's Avatar
 
Member Since: Jun 2004
Location: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Posts: 18,346
Received 767 Likes on 549 Posts

Default

Originally Posted by Wee
Is it safe to say that the black wire (as pictured above) has to be wired to be hot with the switch in the run position and not just when the switch is in the crank position.....Otherwise the car would start but then just go dead....?

The red wire that is not hooked up is made of 8 or so strands of very stiff wire, silver in color. It had a cloth covering most of which is gone but can be seen where enters the rest of the harness, I'm pretty sure it's the wire that is supposed to be hot when the key is in the run position.

So it looks like I have wiring issues to figure out....The battery isn't hooked up so I didn't get a chance to check if the red wire has any power at all.

Brian

OK looks like I need to go read the sticky....I did read an old post between Roger and 69427 about these issues....But it was over my head.
Once the summer activities slow down a bit more I'm planning on writing up a one page summary of the sticky, and then people can read through the rest of the pages if they're interested in greater detail.
I miss Roger's contributions to the forum. He has a lot of experience and good information that he shared with us.
Old 09-10-2015, 10:43 PM
  #13  
69427
Tech Contributor
 
69427's Avatar
 
Member Since: Jun 2004
Location: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Posts: 18,346
Received 767 Likes on 549 Posts

Default

Originally Posted by Big2Bird
(If only)

Hi Mike. Long time.
Darn happy to see your contributions again, Jeff. I hope things are going well with you.
Old 09-11-2015, 08:55 AM
  #14  
jnb5101
Le Mans Master
 
jnb5101's Avatar
 
Member Since: Jul 2006
Location: charlotte north carolina
Posts: 8,117
Likes: 0
Received 100 Likes on 92 Posts

Default

The resistor (ballast or wire) causes a voltage drop. This limits the voltage drop (available voltage ) across the coil. The sum of all voltages in a circuit must equal the supply voltage. The engineers that designed this system knew the resistance and inductance(that's the purpose of the capacitor-it "balances" the counter EMF of the coil and allows faster saturation) of the coil, and chose an external load(resistor) that would limit the voltage drop (and indirectly, following Ohm's Law) the current through the coil. The external resistor can only cause a voltage drop. Voltage and current are tied together, but the purpose of a resistor is to cause a voltage drop, not limit current. Designing a DC circuit while trying to use resistors to "limit" current will never succeed.
Old 09-11-2015, 09:01 AM
  #15  
69427
Tech Contributor
 
69427's Avatar
 
Member Since: Jun 2004
Location: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Posts: 18,346
Received 767 Likes on 549 Posts

Default

Originally Posted by jnb5101
The resistor (ballast or wire) causes a voltage drop. This limits the voltage drop (available voltage ) across the coil. The sum of all voltages in a circuit must equal the supply voltage. The engineers that designed this system knew the resistance and inductance(that's the purpose of the capacitor-it "balances" the counter EMF of the coil and allows faster saturation) of the coil, and chose an external load(resistor) that would limit the voltage drop (and indirectly, following Ohm's Law) the current through the coil. The external resistor can only cause a voltage drop. Voltage and current are tied together, but the purpose of a resistor is to cause a voltage drop, not limit current. Designing a DC circuit while trying to use resistors to "limit" current will never succeed.
Respectfully, please read the Ignition sticky.
Old 09-11-2015, 10:18 AM
  #16  
jnb5101
Le Mans Master
 
jnb5101's Avatar
 
Member Since: Jul 2006
Location: charlotte north carolina
Posts: 8,117
Likes: 0
Received 100 Likes on 92 Posts

Default

PM sent to 69427
Old 09-11-2015, 12:16 PM
  #17  
Wee
Drifting
Thread Starter
 
Wee's Avatar
 
Member Since: Apr 2010
Location: Cartersville GA
Posts: 1,857
Received 333 Likes on 237 Posts

Default

What test/reading am I looking for from the red wire if it is in fact the resistor wire that is supposed to provide running power to the coil.....? Switch off no volts.....Switch in the run position with the motor not running somewhere around 9 volts....?

I know if the black wire has power other than while cranking it is not correct....I don't see anyway it could be correct because the car runs as it is hooked up now.

I looked at the points last night and they don't look burnt to me....I have put around 150 miles on the car over the past 4 months.

Brian

Get notified of new replies

To 1972 350 coil wiring ....?

Old 09-11-2015, 12:55 PM
  #18  
ddawson
Le Mans Master
 
ddawson's Avatar
 
Member Since: Mar 2001
Location: Lincoln, CA
Posts: 5,649
Received 598 Likes on 485 Posts

Default

When I was working on mine and needed to figure out which went were I used a test light.

With the two wires by the starter disconnected I ran a long wire to one and connected the other end to a test light that I could see over the dash.

One would be hot with ignition on. One would only be hot when attempting to start then would turn off when I released the key.

Old 09-11-2015, 12:58 PM
  #19  
Peterbuilt
Le Mans Master
 
Peterbuilt's Avatar
 
Member Since: Aug 2006
Location: mount holly NC
Posts: 6,985
Received 1,244 Likes on 965 Posts
C3 of Year Finalist (appearance mods) 2019

Default The resistor wire limits current not voltage.

Originally Posted by Wee
What test/reading am I looking for from the red wire if it is in fact the resistor wire that is supposed to provide running power to the coil.....? Switch off no volts.....Switch in the run position with the motor not running somewhere around 9 volts....?

I know if the black wire has power other than while cranking it is not correct....I don't see anyway it could be correct because the car runs as it is hooked up now.

I looked at the points last night and they don't look burnt to me....I have put around 150 miles on the car over the past 4 months.

Brian

On this schematic it shows a YELLOW wire between the + terminal of the coil and the "R" terminal on the starter solenoid.
The "R" terminal is the small terminal on the solenoid closest to the fender.
Peel back the black tape and see if your RED wire has a splice or check for continuity from one end to the other.

On the schematic your BLACK wire is shown as BLACK-PINK.
That wire will have 12 volts (battery Voltage) in both START and RUN.

http://www.vetteprojects.com/bmv/mis...tte%201972.pdf


Some time ago 69427 was nice enough to post the reading you should get while testing.
Old 09-11-2015, 01:12 PM
  #20  
Wee
Drifting
Thread Starter
 
Wee's Avatar
 
Member Since: Apr 2010
Location: Cartersville GA
Posts: 1,857
Received 333 Likes on 237 Posts

Default

I was testing last night trying to figure out where the black wire that is now connected at the coil + side ran to....Hooked up the multimeter set to continuity/beep mode took the wire off the coil and clipped one end of the meter to it then started to try wires on the starter but I didn't even make it that far...No matter where I touched it indicated continuity, this is with the negative cable disconnected from the battery. That doesn't seem right to me.

Thank Ya'll for the post above, I'll do more testing tonight.

Brian


Quick Reply: 1972 350 coil wiring ....?



All times are GMT -4. The time now is 09:55 PM.