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1968 Starting Issue

rvrtrash

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Apr 25, 2003
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3,649
OK you electrical folks, how does the brown wire read 12 volts if the pink wire is 8.5 volts?

When the key is turned to start, the starter solenoid energizes, 12V is put through the contacts of the solenoid to the starter cable and the brown wire (#262). That 12V goes through plug D and then the flat 4 prong plug to the coil. It will also go through the resistance wire to the switch, but as the switch is in the start position, the run position contact isn't made and the voltage is just a potential there. When the key is released from the start position and goes to the run position, the starter solenoid disengages and 12V is no longer going to the starter motor or the brown wire terminal through the solenoid. Instead, 12V goes from the switch run position contacts, through the resistance wire, to plug D and the flat 4 prong plug to the coil. Assuming the engine is running, the points complete a circuit through the coil and voltage is dropped to 8-9V by the combined resistance of the coil primary winding and the resistance wire. Voltage will also go out along the brown wire to the starter solenoid terminal, but as the contacts in the solenoid are now open, is just a potential at that point. If the car isn't running, and the points are open, there is no circuit path, no current flow, and you would read 12V at the coil and the starter solenoid terminal. Once the car is running and the points complete the circuit path, you should see the 8-9V. Hopefully this helps. I can make a guess at how the pertronix is built and functions, that would involve a 12V transistor or a 5V transistor and a voltage divider circuit, with a .7 volt base voltage, which is why function is marginal if the resistor wire is used as a power source, but I would be guessing.

Steve
 
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Mosesatm

Mosesatm

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Yep, I get all that, so how does Neil get 12 volts at the solenoid brown wire terminal? That's what I can't figure out because the way I read the wiring diagram it shouldn't be possible.
 

p51

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OK you electrical folks, how does the brown wire read 12 volts if the pink wire is 8.5 volts?

From the schematics I don't see how they can be at different voltages.

When starting, both "S" and "C" on the switch are at 12v (battery voltage). When running only "C" is at 12v and "S" is open.

The wires are both at 12v when starting because of the relay being closed by control signal "S" = 32 which forces 12v on wire 262 (= 16A = 16B = 16).

They are both at ~8.5v when running because "S" is open which leaves the relay open and the 12v is only being supplied from point "C" on the switch. This voltage is then divided down to ~8.5v by the resistor on 16A and the resistor in the coil.
 

p51

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Yep, I get all that, so how does Neil get 12 volts at the solenoid brown wire terminal? That's what I can't figure out because the way I read the wiring diagram it shouldn't be possible.

Well when I looked at the picture it (after rotating it) it sure looked like 10v to me. If the alternator were charging to say 14v then you would be seeing some sort of resistive drop. Caveat: I'm of the generation of digital readouts so I may have been misreading the picture...

Edit:
A little math (3ohm/4.5ohm)*14v = 9.3v. Now with the coil switching on and off the average resistance of the coil will *look* higher than 3ohm... that might make up the difference...
 

franklinair

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Mar 1, 2007
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The check I did today was a static test: Ign Sw in the RUN position (Engine not running). My old reliable Simpson VOM read 12V on the Solenoid small stud.
Tomorrow I'll do the same test with the engine running, and see what I read.
BTW, this CS has a Pertronix system with a 40KV coil.

Neil
 

p51

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The check I did today was a static test: Ign Sw in the RUN position (Engine not running). My old reliable Simpson VOM read 12V on the Solenoid small stud.
Tomorrow I'll do the same test with the engine running, and see what I read.
BTW, this CS has a Pertronix system with a 40KV coil.

Neil

Neil

OK. Got it. Can't be a charging artifact then. But I keep looking at that photo of your multimeter and it looks like the needle is pegged right over 10v to me... I feel like I'm playing "Where's Waldo" and I'm losing badly :wink:

James
 

TraveledGTCS

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Nov 24, 2004
Messages
174
I'm wondering as it looks like you've checked out the ignition switch and such, could it be a bad wire from the switch to the coil or whatever? I had a wire which looked whole but it had a broken wire but the coating was still solid. Somehow it got crimped and separated the wire but not the coating. Luckily there were only two wires I had to worry about and I ended up checking both separate and found the break, it had me going for a while though.

Just a thought.

Bill
 
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Mosesatm

Mosesatm

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That would work, but it's something else to remember to do to start or shut the car off. I also wouldn't really consider it an extra layer of security, because a '68 is super easy to get started without a key anyway.
{snip}

Steve

Yep, all that’s needed to start one is a pair of pliers (without rubber handles) and three feet of wire, even if the coil wire is pulled.
Another advantage of the Pertronix system is that the ring is easily removed. Pulling it makes the car unstartable, unless the thief happens to have a replacement. The Pertronix and a fake coil wire should stop most people with larceny on their minds.
 
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robert campbell

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Apr 10, 2007
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4,321
Neil,
I think that post is fed from the ignition circuit, and since there’s something wrong with my ignition circuit I can’t use the post as a coil feed.

The post closest to the starter cable is not fed by the ignition. It is only hot when the key is in the start position. Its purpose is to provide 12 volts to the ignition system when the starter is engaged to assist in the start up. When the key is released to the run position this post is dead.

Neil, what is that coil doing on the shock tower??

This thread is killing me!! Do I need to come over and fix it!!

Rob
 
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Mosesatm

Mosesatm

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Rob,
You should realize that we do this just to annoy you.:grin:
 

franklinair

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I did a re-check on Stephen's CS re: the 'Run' voltage readings I'm getting. I used my digital meter for the sake of accuracy, and her's what I got.
This is for the Brown wire to the Solenoid:
Ign Sw in RUN position (engine not running)= 5.8V
Ign Sw in RUN position (engine running)= 10.8V

Rob- The coil was/is mounted on the shock tower, relocated by the P/O. When I installed the Edelbock 4BBL intake & Carb there is not sufficient clearance to mount the coil in the correct location.
Stephen had named his CS 'Doug'. My name for it is 'Christine', if you get my meaning.:wink:However, now all the maladies (suspension, engine, electrical, heater & A/C, cosmetics) have been addressed.

Neil
 

p51

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Aug 2, 2005
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Location
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I did a re-check on Stephen's CS re: the 'Run' voltage readings I'm getting. I used my digital meter for the sake of accuracy, and her's what I got.
This is for the Brown wire to the Solenoid:
Ign Sw in RUN position (engine not running)= 5.8V
Ign Sw in RUN position (engine running)= 10.8V

Rob- The coil was/is mounted on the shock tower, relocated by the P/O. When I installed the Edelbock 4BBL intake & Carb there is not sufficient clearance to mount the coil in the correct location.
Stephen had named his CS 'Doug'. My name for it is 'Christine', if you get my meaning.:wink:However, now all the maladies (suspension, engine, electrical, heater & A/C, cosmetics) have been addressed.

Neil

Neil

Thanks for taking the measurements.

Re: "Ign Sw in RUN position (engine not running)= 5.8V"

This is actually lower than I would have expected. I was expecting 6.25v at least. Are you using that wire to provide power to any other loads other than coil and the ignitor1... such as the Edelbrock carb electric choke circuit or something similar?

Thanks
James
 

rvrtrash

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Apr 25, 2003
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3,649
This thread is killing me!! Do I need to come over and fix it!!

Rob

I'm with you Rob! I'm about done talking and just waiting for Arlie to tell me to come over and get it fixed. Maybe you should show up too and we can tell Arlie to go make a beer run while we see what mischief we can create with his car. :grin:

Steve
 

Ruppstang

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May 22, 2009
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I am with you guys, if it was not 1800 miles I would all ready have been on my way!
 

robert campbell

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Apr 10, 2007
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I'm with you Rob! I'm about done talking and just waiting for Arlie to tell me to come over and get it fixed. Maybe you should show up too and we can tell Arlie to go make a beer run while we see what mischief we can create with his car. :grin:

Steve

As long as the beer is dark and smooth!!!
 

p51

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Arlie

So?.... did you ever figure out what the problem was? How did you finally fix it?
Just curious.

James
 
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Mosesatm

Mosesatm

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I’ve was on vacation last week so I hadn’t thought about it for a couple weeks. That said, I think the problem lies with the run wire in the ignition switch connector, or just beyond the connection.

By the way, if anyone wants to take a vacation in Hawaii do it now and go to the Kona side of the big island. Flights actually have open seats at great prices, the golf courses and restaurants are nearly empty, and many vacation rentals are half price or lower. The best part is that the volcano has absolutely no influence on that side of the island, and it’s the side with the good weather and the resorts.
 
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Mosesatm

Mosesatm

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Today I ran a 12V wire to the coil and the car would not start. I then dumped a little gas in the carb and it started right up.

Once the car starts it will start every time, unless it sits for a long time, then no amount of pumping the throttle will get it to start.

The car runs well when it runs.

Any ideas? Maybe a torn fuel pump diaphragm? Is all the gas draining out of the carburetor bowl? Does a 1V even have a bowl?
 
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