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Old 09-15-2020, 09:46 AM   #1
GtoBrian
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1972 C10 Points Ignition Issue.

72 C10 with a 350/350. Problem that started recently, when driving down the road or even just stopped at a light engine would die, no spitting or sputtering just shut off as if you just turned the key off. I have replaced the cap rotor points, coil plugs and wires. This problem was there before parts were replaced. I hooked up my volt meter, when starting it would either show 12 volts or zero, guess depending if points were open or closed? then would start and watch and watch anywhere from 8.2-9.0 or higher when given throttle. After awhile of running in gear with either lights on or turn signal on would watch as the voltage would drop in the 7.5 range then drop to 6.0 and stall. Could this be the resistance wire going bad? It will usually start back up but a few times it would start and die as soon as the key was released from start position , located the wire in my harness at the fuse block but it is not white cloth appears to be a faded pink but runs across the top of the firewall and connects to the 2 yellow wires, 1 going to the coil the other to the R on the solenoid. Any and all help would be greatly appreciated.
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Old 09-15-2020, 11:57 AM   #2
VetteVet
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Re: 1972 C10 Points Ignition Issue.

The resistance wire is fed by the key switch ignition terminal which also feeds the fuse panel cluster fuse. You could have a poor connection on the key switch terminal causing the voltage drop enough to kill the ignition yet not enough to affect the gauges in the cluster. I would check the voltage at the cluster fuse just like you did at the ignition coil and see if you get the drop there. If you do then I would suspect the ignition switch connection. This is a common thing that happens on these old harnesses.

The ignition coil feed (pink wire) also goes directly to the firewall block inside the cab behind the fuse panel. It connects there with the resistor wire which joins the two yellow wires as you have discovered. The yellow wire on the R terminal at the solenoid shunts 12 volts from the battery to the coil as soon as the starter engages, and it disengages as soon as the key is released. This is for a full 12 volts to the coil for cold starts, and it is why the engine dies as soon as you release the key. These connections at the firewall block also corrode and cause increased resistance which leads to voltage drops.

The other yellow wire goes to the coil for 8/9 volts to the coil for normal engine running. This prevents coil burnout and protects the points from arcing and failing prematurely. The resistance wire was originally an orange white purple cloth covered wire which fades over time as yours has. The diagram below shows the wiring path.



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Here is the ignition switch wiring. The 12 gauge pink wire is the ignition wire.


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Here is the wiring showing the ignition wire going to the firewall block and the fuse panel.



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You should also check the output of the alternator to be sure it is providing the right amount of voltage at all times. The battery should keep the ignition running even if the alternator output is low, but is can't hurt to check it.

Three of the best mods we can do to our old trucks is, Converting to an internally regulated alternator, HEI ignition. and headlight relays. These are very easy and relatively cheap to do. There are tons of how to s. on this forum to help.

If you want a test of the resistance wire just get a 1.8 ohm ballast resistor from the auto parts guys and run it in series with a wire from the fuse panel IGN UNfused terminal to the positive side of the coil. You can leave the other wire on or run a new wire from the starter R terminal.
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Old 09-15-2020, 12:03 PM   #3
VetteVet
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Re: 1972 C10 Points Ignition Issue.

Quote:
Originally Posted by GtoBrian View Post
72 C10 with a 350/350. Problem that started recently, when driving down the road or even just stopped at a light engine would die, no spitting or sputtering just shut off as if you just turned the key off. I have replaced the cap rotor points, coil plugs and wires. This problem was there before parts were replaced. I hooked up my volt meter, when starting it would either show 12 volts or zero, guess depending if points were open or closed? then would start and watch and watch anywhere from 8.2-9.0 or higher when given throttle. After awhile of running in gear with either lights on or turn signal on would watch as the voltage would drop in the 7.5 range then drop to 6.0 and stall. Could this be the resistance wire going bad? It will usually start back up but a few times it would start and die as soon as the key was released from start position , located the wire in my harness at the fuse block but it is not white cloth appears to be a faded pink but runs across the top of the firewall and connects to the 2 yellow wires, 1 going to the coil the other to the R on the solenoid. Any and all help would be greatly appreciated.


The red is why I suggested to check the alternator or voltage regulator.
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Old 09-15-2020, 12:31 PM   #4
GtoBrian
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Re: 1972 C10 Points Ignition Issue.

Quote:
Originally Posted by VetteVet View Post
The red is why I suggested to check the alternator or voltage regulator.
I was thinking that also, I will check the ignition fuse on the fuse block and also unplug the fuse block connector from the engine side and check for corrosion, I did swap in a good used ignition switch as the one i had in the truck felt kinda worn out to me, I will do some more testing as soon as i can and let you know, Thank you.
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Old 09-15-2020, 12:42 PM   #5
GtoBrian
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Re: 1972 C10 Points Ignition Issue.

Quote:
Originally Posted by VetteVet View Post
The resistance wire is fed by the key switch ignition terminal which also feeds the fuse panel cluster fuse. You could have a poor connection on the key switch terminal causing the voltage drop enough to kill the ignition yet not enough to affect the gauges in the cluster. I would check the voltage at the cluster fuse just like you did at the ignition coil and see if you get the drop there. If you do then I would suspect the ignition switch connection. This is a common thing that happens on these old harnesses.

The ignition coil feed (pink wire) also goes directly to the firewall block inside the cab behind the fuse panel. It connects there with the resistor wire which joins the two yellow wires as you have discovered. The yellow wire on the R terminal at the solenoid shunts 12 volts from the battery to the coil as soon as the starter engages, and it disengages as soon as the key is released. This is for a full 12 volts to the coil for cold starts, and it is why the engine dies as soon as you release the key. These connections at the firewall block also corrode and cause increased resistance which leads to voltage drops.

The other yellow wire goes to the coil for 8/9 volts to the coil for normal engine running. This prevents coil burnout and protects the points from arcing and failing prematurely. The resistance wire was originally an orange white purple cloth covered wire which fades over time as yours has. The diagram below shows the wiring path.



Attachment 2048313


Here is the ignition switch wiring. The 12 gauge pink wire is the ignition wire.


Attachment 2048314



Here is the wiring showing the ignition wire going to the firewall block and the fuse panel.



Attachment 2048315


You should also check the output of the alternator to be sure it is providing the right amount of voltage at all times. The battery should keep the ignition running even if the alternator output is low, but is can't hurt to check it.

Three of the best mods we can do to our old trucks is, Converting to an internally regulated alternator, HEI ignition. and headlight relays. These are very easy and relatively cheap to do. There are tons of how to s. on this forum to help.

If you want a test of the resistance wire just get a 1.8 ohm ballast resistor from the auto parts guys and run it in series with a wire from the fuse panel IGN UNfused terminal to the positive side of the coil. You can leave the other wire on or run a new wire from the starter R terminal.
The IGN UNFused terminal on my fuse box has a thick Pink wire that runs through a hole in the fire wall and upon tracing it, goes to the Idle kick up solenoid mounted on my quadrajet carb. Was thinking if i do convert to HEI then that is where i would need to pull 12V from.
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Old 09-15-2020, 02:04 PM   #6
VetteVet
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Re: 1972 C10 Points Ignition Issue.

You could do that . The IGN UNFused slot is where most of the guys take their power from but here is a great write-up for a clean conversion.

http://67-72chevytrucks.com/vboard/s...d.php?t=708975
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Old 09-15-2020, 03:37 PM   #7
GtoBrian
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Re: 1972 C10 Points Ignition Issue.

As far as the rest of my troubleshooting, first i had swapped a known good ignition switch which feels tighter , my orig felt real easy to turn between start and run, second checked my fuse block engine side, 3/8 bolt was actually loose could back it of with just the extention and socket. No corrosion found put it back together and snugged tight. I unplugged the pink power wire that was in my IGN UNFUSED terminal left it unplugged and with key on verified 12 volts at all of my fuses including the spade terminal for IGN. Started truck with 1 voltmeter on battery charging 14.3-14.5 volts consistent turning all accessories on and off at the same time another voltmeter hooked to coil with all accessories on and volts at coil stayed 9.6-10.0 never dropping in the 8 volt range. Ran for about 45 mins like this so not really sure if the ign switch was the problem or if i really havnt found it yet, dwell is steady at 30, idle 650 in gear, guess i will see when i take it for a test drive when the weather clears. Obviously open to any more things to check or ideas, Thank you.
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Old 09-19-2020, 12:46 PM   #8
Dead Parrot
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Re: 1972 C10 Points Ignition Issue.

A bad condenser can cause all sorts of problems with an points system. Don't assume a new one is good. A friend and I learned that one the hard way after spending two days chasing a 'runs like crap' problem. He had already replaced the points and condenser but when he got a 2nd new set, the motor returned to its normal happy self.
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