Truck Won't Run

[Bunkythe3rd]

I am having an issue where I go to turn my truck on and the motor will start when on the starter but when the key returns to the run position I lose spark. The motor then spins down to a stop. I put a timing light on it to verify there was no spark.

One other thing to note is, I was having an issue with the motor stalling out before not starting so I did replace the carburetor during this time to rule out fuel.

Now the stuff I have replace. I have replaced the ingnition switch and the ignition coil. What else should I test or replace?

The fact it is running when on the starter and actually over runs it has me stumped. I have attached photos of the switch and distributor just in case it is something as stupid as a wire is missing.

Thank you to everyone in advance.

[dmb]

you have the wrong wire hooked to the distributor come off the switchs terminal that that says ign or dist run a new wire as the one on it may be a resister wire

[Bunkythe3rd]

I should also mention i believe this is a later model chevy 350 crate engine. That is the only reason I was thinking it wasn't that the resistor wire was left in but I will have to check because this is how I got it.

What makes you think it is the resistor wire? Is there a marking on it?

Thank you

[dmb]

they had a resister wire on the gms up to electronic ign. A yellow wire came off the starter solenoid to the coil to give it 12 volts while cranking and when the switch was turned back to run it would run off the wire from the switch with resistance in it
you did not say what truck you are working on

[dmb]

you have to have 12 vlts at the dist with the switch on, I dont think you have it there. you can check it with a test light

[RustyPile]

A resistor wire has a solid conductor, not strands. Also, the insulation is cloth-like, not vinyl. The wire cannot be soldered, solder will not stick..

[Bunkythe3rd]

Ok, so if the yellow wire is the 12 volts to the starter, which one is the resistor wire? Is it part of the connector in the back?

Oh also it is a 1969 Chevy C20 by Vin. It has a 67 front end on it.

[HO455]

Originally Posted by Bunkythe3rd

Ok, so if the yellow wire is the 12 volts to the starter, which one is the resistor wire? Is it part of the connector in the back?

Oh also it is a 1969 Chevy C20 by Vin. It has a 67 front end on it.

Think of it this way. The yellow wire is actually 12 volts FROM the starter when it is energized.

As it came from the factory your truck's ignition coil was designed to run on 8 volts. (Approximately thereabouts) That 8 volts was created by supplying 12 volts to the "Resistor wire" (Also commonly referred to as a Ballast wire) from the ignition switch. Just like a resistor in an electronic circuit the "Resistor wire" drops voltage by a certain amount depending on how it was manufactured.

When starting the engine the voltage available from the battery will drop. It can go as low as 9 to 10 volts. When that happens the 8 volts at the coil drops too. It may drop too low to make enough spark to start the engine.

So to solve this condition GM (And many others) added a terminal to the starter to supply 12 volts to the coil when the starter was energized. That wire is the yellow wire on your truck.

That yellow wire and the ballast wire were usually connected at the coil. Not having the "Resistor wire" or a suitable replacement connected to the coil means the coil is only getting power when the starter is energized. Shut the starter off and the coil is no longer powered and the engine dies.

HEI ignitions were designed to use 12 volts so the "Resistor wire" disappeared from GM vehicles at that time.

Hope this helps.

[RustyPile]

I thought I gave a pretty good description of those wires.. OK, I'll try again.. The resistor wire runs from the coil through the harness to the firewall plug. It is readily identifiable as the insulation is cloth like instead of the normal vinyl. Also, it will probably have a faded appearance.. And as you stated, the yellow wire runs from the coil down to the starter.. The 2 wires are joined together at the coil terminal..

Remove both wires, they're not needed, especially the yellow wire as it is "HOT" when the ignition is ON... Separate the firewall connector by removing the bolt in the center. Using needle nose pliers, reach in and grasp the terminal on the edges and squeeze it.. This releases the "catch" and the terminal can be removed. Here is a link to the replacement terminal.. No need to order online, most parts stores have them in stock.

https://www.classicindustries.com/pr...1069ea6c9cfcda

[EDIT] Here is a link to the proper terminal and plug for connecting the new ignition wire to an HEI...

https://www.summitracing.com/parts/s...+5ca6324dae5a6

[Bunkythe3rd]

You did give a good description. The truck is not where I am currently so I am trying to gather my understanding through the pictures.

Thank you for the help.

[RustyPile]

Originally Posted by Bunkythe3rd

You did give a good description. The truck is not where I am currently so I am trying to gather my understanding through the pictures.

Thank you for the help.

Bunky, this electrical forum has an assortment of wiring diagram threads that are free to download. They're in color so you can easily trace the circuits on them.. I suggest you pick the one that "fits" your truck, download it and refer to it when you go after this run problem..

[Bunkythe3rd]

I have found the electrical schematics and a nice thread on how to replace the resistor wire

[VetteVet]

Here is one of the firewall terminal and a partial wiring diagram

[Willshook]

I would just grab a 12V off the IGN UNFUSED terminal on the fuse box and run it direct to the HEI. Super simple.