Thread: No spark
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Old July 12th, 2017, 11:44 PM
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Default Re: No spark

The reason you need two wires to coil (your possible problem), the need for a "12V to coil" check, before cranking and during cranking, and a visual inspection of the coil positive wiring, is described below:

One wire to coil comes from the starter solenoid "R" terminal and it provides 12V to coil while starting. It is only live when ignition switch is in the start (spring loaded/far right) position. It shuts off when you let go of switch. That is when the second wire takes over. This is the other wire that should be on the coil positive post. It is the resistor/resistance wire. It comes from the ignition switch when the ignition switch is in the "run" position or "on" position. It has a reduced voltage of only about 8-9 V. It's a "special" wire material and a specific length. It is wrapped back and forth on itself inside the harness bundle.

If you are missing the "R" wire from solenoid, then the other wire may not provide enough spark because as the starter needs all 12V. This wire, with only 8V, may loose more and not supply hot enough spark, thru coil, to plugs.
If you are missing the resistor wire, you won't have ANY voltage to coil after you let go of starter. If you were missing this wire, the truck should start and then die after you let go of switch. SOoooooo if you are missing the "R" solenoid wire or one of these two wires is mis wired to the wrong place, OR IGNITION SWITCH IS MIS WIRED, that could be the problem. So study the schematic and trace each wire to see where it goes AND SEE THAT THEY ARE STILL CONNECTED TO WHAT I SAID.
Not yelling, emphasizing.

Also the negative coil wire goes to the distributor, be sure that is wired correctly. That wire goes to the points pinch post, same place the condenser wire goes.

Where does the negative battery cable go? To somewhere on the motor?

Do you have a white ceramic block on the firewall anywhere?
Like This?

Ignition switch wiring: Terminal marked "BATT" = wire directly from battery.
Terminal marked "Start" or "Sol" = goes to "S" terminal on solenoid.
Terminal marked "IGN" or "ON" = goes to coil pos. Again, some of this wire is the resistor wire.
These wires may go thru connectors or be passed thru junction blocks but do go where I indicated, eventually.
The ignition switch has a "ACC" terminal for accessories. The wire should go to the fuse box.
Some of the terminals I've listed on the ignition switch may have other wires connected to them. Try to determine that they are not interfering with anything we are doing.
Take your time, you have a lot to absorb and think about, but you are smart and none of it is difficult, just new to you. Eventually we will trace down the miswire, broken wire, bad component, adjustment error, missing wire, missing part.
I still don't know if you disconnected a wire during A/C install, or didn't install points correctly, did some other "work" you forgot you did or you didn't do anything wrong.


Don't take this the wrong way but I don't know what you know: You do know that when you check the spark plug it is out of the hole with the wire still attached and the MOTOR IS CRANKING OVER and you look for spark snapping/arcing across the gap at the threaded end, every revolution, Right? It has to be touching the unpainted, not greasy part of the motor. With all the coil and distributor wires hooked up.

"I did find a bad connection on the starter that I fixed." EXPLAIN this in detail!!!!! Answer ALL questions. underlined to enable us to think it thru. Not as interrogation or blaming.

Last edited by AZKen; July 13th, 2017 at 09:43 PM.
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