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2/19/17 4:43pm - Original Message: 'How to get 'Key On' 12 volt at the coil?'
Christian
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Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 154
I currently get 6 volt at the +terminal of the coil, which is what I am supposed to get when not cranking. It comes from the outer terminal of the starter solenoid. It is my understanding that the voltage is downgraded from 12 volt to 6 volt by the wire itself which is supposed to be a resistance wire.
I want to install a Pertronix Ignitor III with the Flame-Thrower III coil that needs 12 volt; I thought I just have to run a regular 12-Ga wire from the same terminal on the starter solenoid to the coil's +terminal. Checking with a multimeter, I only get 6 volt at that solenoid terminal with the key on (0 with the key off), but I have 12 volts at the main terminal were the battery cable is connected.
Does it mean that the existing wire is no a resistant wire? How do I get 12 volt to the coil?
Thanks for your help.



|UPDATED|2/19/2017 1:43:09 PM (AZT)|/UPDATED|
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2/19/17 10:42pm - Reply: 'Re: How to get 'Key On' 12 volt at the coil?'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
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The voltage drop for the ignition coil is due to a resistor wire, but it comes from the ignition switch, not the starter terminal. The wire from the starter "R" terminal provides full battery voltage while cranking only. Once the key is returned to the "Run" position, the ignition is powered by the resistor wire.
To get full battery voltage at the new coil set-up, you will need to tie into a wire coming off of the ignition switch that is hot with the key in the "Run" position, and keep the yellow wire from the starter solenoid "R" terminal connected. Thumbs Up

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2/19/17 11:08pm - Reply: 'Re: How to get 'Key On' 12 volt at the coil?'
Christian
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Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 154
Thanks. If I follow the wire that is connected to the +terminal of the coil, I arrive at  the starter solenoid. The outer terminal shows +6 volt with the key on the on position (zero with the key off). The inner terminal shows 0 volt and I believe that is the one that provides 12 volt when cranking (I was on my own and unable to test that).
Where typically would you take the 12 volt feed?

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3/3/17 12:51pm - Reply: 'Re: How to get 'Key On' 12 volt at the coil?'
Sobmstr
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Georgetown, TX - USA

Vette(s):
1968 327/350 original unrestored

Joined: 9/3/2016
Posts: 2
Christian,
 
There should be two wires connected to the + terminal of the coil, both wires typically crimped into the same connecter terminal.
1) cloth type of insulation from the ignition switch via the bulkhead connecter.  This is a resistor wire to limit voltage to the points when running (approx. 9.6v).  The reduced voltage keeps the points from burning prematurely.
2) second wire (usually yellow) goes to the outer R terminal of the starter solenoid to provide batt voltage during cranking. since Batt voltage typically drops to 10-10.5v during cranking this full voltage is needed to run.
 
If you're doing much wiring on the car I suggest getting laminated wire diagrams from Dr.Rebuild, they are much better than original GM.
 
Good luck!
Rich
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3/4/17 6:13pm - Reply: 'Re: How to get 'Key On' 12 volt at the coil?'
Christian
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Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 154
Thank you Rich. You are correct, there are two wires to the + at the coil. Not easy to see because they are wrapped together in the same black cloth-like sleeve at this point.
According to the electrical diagram, the one that goes to the ignition switch via the bulkhead connector is 20g and is black and then red-white and has a fusible link somewhere between the coil and the bulkhead connector.
Past the bulk head connector, it is a 12g pink wire to the ignition switch .
Several questions:
1) I can't locate the bulkhead connector under the dash: Where exactly should I look for it?
2) Do you know if the drop in voltage is done between the bulk head connector and the coil (in which case, I would need to bypass that wire between the coil and the connector), or if I need to bypass the pink wire to the ignition switch as well? I tend to believe the 12g wire is probably not the resistor wire.
3) The whole purpose of bypassing the resistor wire is to get 12 volts at the coil. Doing this, I would also bypass the fusible link. It does not sound like a bright idea. Your thoughts?


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3/4/17 8:21pm - Reply: 'Re: How to get 'Key On' 12 volt at the coil?'
Christian
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Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 154
OK. As to the location of the bulkhead connector, I got some clues.
If I understand well, it makes the connection through the firewall, just behind the fuse box.
How do I access this connector? Considering I am working on the engine compartment side, I am interested in accessing that side of the bulkhead connector.


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3/8/17 5:32pm - Reply: 'Re: How to get 'Key On' 12 volt at the coil?'
jeffs74coupe
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Fairfield, PA - USA

Vette(s):
1974 Stingray coupe 350/automatic

Joined: 9/16/2016
Posts: 8
If your 71 is the same as my 74, you can get 12V at the idle stop solenoid whenever the key is on.

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3/10/17 3:09pm - Reply: 'Re: How to get 'Key On' 12 volt at the coil?'
nosal1 Gold Member
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Dunedin, FL - USA

Vette(s):
1980 Corvette Torch Red with Gold metallic 370HP/350 CU.IN.Turbo 350 w/shift kit.Originally CA.Car with 305 CU.IN.

Joined: 3/21/2006
Posts: 230
Christian,
      First question are you changing from points distributor to a HEI Type distributor,if so then you have relief coming,i.e....Look under the dash to the fuse block,put your glasses on and bright small flashlight..You will be looking for a place labeled IGN fused or unfused that will have two flat pins you can slide on a spade with #12 -14 gauge wire (preferably red) and find a hole to run this wire through the firewall,which should be long enough to reach the HEI distributor ('75-"80 OEM Chevy dist.) and install a spade on the end and slide it onto the + side of the HEI dist. and also your TACH.
There is NO power at the IGN spades until you turn key to run/start position.
Now if you stay with the points system then you have what you have,however YELLOW wire is to the R on solenoid,terminal close to the exhaust and the PURPLE wire to S terminal closest to the block( GM did not want it to easy for you to connect this wire ...  Have fun and a Great day.....Sal C          nosal1


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3/11/17 4:17am - Reply: 'Re: How to get 'Key On' 12 volt at the coil?'
nosal1 Gold Member
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Dunedin, FL - USA

Vette(s):
1980 Corvette Torch Red with Gold metallic 370HP/350 CU.IN.Turbo 350 w/shift kit.Originally CA.Car with 305 CU.IN.

Joined: 3/21/2006
Posts: 230

A quick note to you .If in fact you go with Ignitor III,one of my favorite electronic ignitions systems,you will have to use,install a Pertronix .32 OHM coil,which is required for Ignitor III,as is 1.6 ohm for Ignitor II,and Ignitor I needs 2.8 -3.2 coil..Follow my instructions on running new wire from inside fuse block and you will be a happy camper..       nosal1         Sal C



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3/11/17 11:45am - Reply: 'Re: How to get 'Key On' 12 volt at the coil?'
Christian
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Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 154
Thank you for the valuable information. Yes, I am installing the Ignitor III and yes, I have the special coil that goes with it. The access to the fuse box is everything but easy (I am rather tall and my arms are a little too long between the elbows and the wrist to give me much liberty with my hands in there). I was trying to find a more accessible place to get the 12 volt key on. But I will follow your instructions. I have got to find a way. Thanks a lot.

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3/11/17 3:05pm - Reply: 'Re: How to get 'Key On' 12 volt at the coil?'
nosal1 Gold Member
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Dunedin, FL - USA

Vette(s):
1980 Corvette Torch Red with Gold metallic 370HP/350 CU.IN.Turbo 350 w/shift kit.Originally CA.Car with 305 CU.IN.

Joined: 3/21/2006
Posts: 230

Christian,

I feel your pain.. I am the opposite, in that I am short,short arms and very Stocky,which makes it difficult for me to do the under dash work..I have a long ,long nose needle nose pliers which come in handy..In any event I wish you success.        Sal C                  nosal1


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3/13/17 8:47am - Reply: 'Re: How to get 'Key On' 12 volt at the coil?'
Christian
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Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 154
I installed both the Iginitor III and the Pertronix Flame Thrower coil, following your directions.
It just works great.
Fires up better, idles better, cruises in 4th gear at 25 mph better than ever.
Can't really tell the difference at high RPM but the thing just works great generally speaking.
Thank you for your help.



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3/16/17 4:02am - Reply: 'Re: How to get 'Key On' 12 volt at the coil?'
nosal1 Gold Member
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Dunedin, FL - USA

Vette(s):
1980 Corvette Torch Red with Gold metallic 370HP/350 CU.IN.Turbo 350 w/shift kit.Originally CA.Car with 305 CU.IN.

Joined: 3/21/2006
Posts: 230

Your welcome Christian my pleasure and Happy Motoring..Sal C      nosal1



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