cranks but no spark

philldron

Member
Nov 17, 2020
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54
kennewick wa
Ive got a recently completely restored daily driver 68 Coupe 302 4 bbl Holley with a Pertronix in the distributor. I went out to start it after work the other day and it would only turn over. Ive done several diagnostics. heres where I am at; its not a fuel issue. No spark on plug. Power on both sides of coil, I ran a jumper from flame thrower coil+ to + on Battery and it started right up..
The engine wire connection at firewall is tight.
So, Ive bought a new ignition switch(the previous one was only a few months old....) Ill replace it to see if thats the issue. What else could it be?
I was going to test the positive side of coil while cranking engine to see if it still has 12V to see if the coil is bad(not sure how else to test for a bad coil??)
Engine wire is new, if I unplug it to check for power going through from pig tail at firewall, If I check the pig tail coming out of firewall on crank/start should I be reading 12 V on just the male prong or in both the female plug holes or some other combo?
IF the ignition switch is good but theres not power on start going through to fire wall side of plug, remedies??(I seriously dont want to have to replace a dash harness...)
thanks everyone, this is my first post but Ive read lots of others posts ovr the last few years for help as I restore my mustangs
 
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wicked93gs

10 Year Member
Sep 30, 2006
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Nashville TN
66+ignition,+starting+and+chargimg.jpg


This is for a '66. but I would be shocked if '68 was much different. Essentially the coil pulls its 12v+ from the hot-in-run/start terminal on the ignition switch so it is always powered as long as the car is on.
 

philldron

Member
Nov 17, 2020
2
1
13
54
kennewick wa
66+ignition,+starting+and+chargimg.jpg


This is for a '66. but I would be shocked if '68 was much different. Essentially the coil pulls its 12v+ from the hot-in-run/start terminal on the ignition switch so it is always powered as long as the car is on.
Thanks for the diagram!

So to help the next guy: I did one more diagnostic check, I got my multimeter on the + coil and had my kid crank the motor, the volts went from 12V down to 3-4 volts. Same measurement on the solenoid. I figured it must be the solenoid then, went and put a new one on and it started right up(Solenoid was only a few months old....so either I got a bad one or something else messed it up.) either way Im back on the ROAD!!
 
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wicked93gs

10 Year Member
Sep 30, 2006
1,106
179
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Nashville TN
Yeah....in my old 67 I would kill a solenoid every 6 months or so...first thing you do is jump across the solenoid with a screwdriver to test it.
 

rbancy

Member
May 12, 2020
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Victoria, BC, Canada
check the cranking voltage. Get someone to crank it and see how many volts your getting when it cranks. What does it drop down to ? Sometimes could be the resistor. Had same problem with mine before.