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Starting issue
#1
Ok guys, gotta strange electrical issue going on with my 72 Mach 1. This is the car that I got in the accident with. Anyway, I will try my best to explain this. 
After having everything rebuilt and put back together, the engine will not fire after sitting overnight. When the solenoid is jumped, then it does start and runs great. It will even fire right back up without jumping the solenoid. So the shop replaced the solenoid I had on with a new one. Same thing, solenoid has to be jumped to start for the first time of the day, but once it’s been started it will start over and over again. The coil is brand new also cause the one I had didn’t work after the accident. The shop owner who has been working on Mustangs for 30 plus years is stumped, he has never seen anything like this before.
Any idea of what to look for? The NNS is only a couple of years old, adjusted properly and in great shape. Maybe the ignition switch? 
The only wiring that was damaged from the accident was the drivers side sport lamp, turn signal ,headlight and a headlight wiring relay harness. Thanks, any ideas will be appreciated

run_horse Run Horse Run!
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#2
Maybe they should systematically backtrack all the way to the ignition switch jumping one item at the time. Jump the NSS, jump the switch, etc, until they find the culprit. At least that would be my approach.

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1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump
4-wheel disc brakes
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#3
When you say won't fire, does the starter turn the engine over? Or does the starter not function, nor the solenoid even click? I'm guessing the starter and solenoid don't work. Easy enough to verify where the issue is. With the ignition key held in the start position check for voltage on the "S" terminal on the starter solenoid.

My guess is that the ignition switch is the culprit. After sitting for some time, while the car was repaired, the decades old ignition switch terminals are likely corroded and the lubricant in them has turned semi-solid, preventing the contacts in the switch from making connection. After the car has started the vibrations and/or heat generated by bad contacts in the switch allows the starter contacts to make connection.

Added: It could be the same issue with the NSS, just less likely because it is newer and was functioning before the crash.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#4
(04-04-2019, 04:34 PM)Don C Wrote: When you say won't fire, does the starter turn the engine over? Or does the starter not function, nor the solenoid even click? I'm guessing the starter and solenoid don't work. Easy enough to verify where the issue is. With the ignition key held in the start position check for voltage on the "S" terminal on the starter solenoid.

My guess is that the ignition switch is the culprit. After sitting for some time, while the car was repaired, the decades old ignition switch terminals are likely corroded and the lubricant in them has turned semi-solid, preventing the contacts in the switch from making connection. After the car has started the vibrations and/or heat generated by bad contacts in the switch allows the starter contacts to make connection.

The starter does spin, but no spark, no power to coil.

I’m leaning towards the ignition switch too. Most everything else on my car has been replaced and or rebuilt except that. I had to replace the brake light switch about a year or so ago and it was the original one. I noticed that the ignition switch also looked like it was the original one too. I just didn’t know if it would show these symptoms. 
Thanks Don, I will let them know to try that first and I’ll post results.

run_horse Run Horse Run!
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#5
(04-04-2019, 04:26 PM)tony-muscle Wrote: Maybe they should systematically backtrack all the way to the ignition switch jumping one item at the time. Jump the NSS, jump the switch, etc, until they find the culprit. At least that would be my approach.

Sent from my SAMSUNG-SM-G930A using Tapatalk

Ya that’s what needs to be done, and I think I will have them start with the ignition switch.
Thanks tony.

run_horse Run Horse Run!
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#6
If it is the ignition switch, then jumpering the starter solenoid won't cause it not to give voltage to the coil. From your description, the starter solenoid gets the signal to crank the starter, but won't give voltage to the coil line. When the starter is engaged, so is the line from the starter solenoid (sorta) directly to the coil, bypassing the ignition switch circuitry. The car should catch, but if the ignition switch is dead or inoperable, the engine would die. That's not what you're describing.

Using your ignition switch, remove the I lead from the starter switch and see if you have 12V there when cranking. If so, re-attach and remove the lead to the coil, and test there for 12V. If no 12V, you have bad circuitry in your headlight harness (which those wires do route to the left side of the engine compartment). My guess is you have a bad splice somewhere that is flakey.

When you first stated it wouldn't start sitting overnight, my first thought was a bad battery. It still could be that, but you say the starter does crank. Check to see what the voltage is at the battery while cranking. If it drops much below 10.5V, you won't be able to start the car.

Let me check your shorts!
http://midlifeharness.com

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#7
Since they had the whole car apart and engine out, verify you have a proper battery (-) -> fender apron -> block ground cable. If this is not done properly, or is missing the fender apron ground, you'll have all sorts of odd electrical issues.


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#8
i 100% agree with midlife. those few points will give u a ton of info. this will take just a few minutes so in doing this report back the info found..
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#9
jpaz, 
sounds to me like your ignition is capable of firing in the run mode but not in the crank mode.
They are 2 different circuits.
your results are all based on how the car was tested, when you are jumping the solenoid with the key in the run position you are not testing the crank circuit.
You need to test the crank circuit.
check for spark while someone is actually cranking the engine using the ignition switch (key) and Not jumping the starter solenoid.
You will find you have spark in run and no spark in crank.
Spark in the CRANK circuit is provided by the I terminal of the starter relay, first thing, you need to have voltage on that terminal while cranking, then you need to have voltage to the coil positive while cranking, will check the 1972 wiring guide and give you circuit number, color and splice location.
Boilermaster
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#10
(04-04-2019, 07:26 PM)midlife Wrote: If it is the ignition switch, then jumpering the starter solenoid won't cause it not to give voltage to the coil.  From your description, the starter solenoid gets the signal to crank the starter, but won't give voltage to the coil line.  When the starter is engaged, so is the line from the starter solenoid (sorta) directly to the coil, bypassing the ignition switch circuitry.  The car should catch, but if the ignition switch is dead or inoperable, the engine would die.  That's not what you're describing.

Using your ignition switch, remove the I lead from the starter switch and see if you have 12V there when cranking.  If so, re-attach and remove the lead to the coil, and test there for 12V.  If no 12V, you have bad circuitry in your headlight harness (which those wires do route to the left side of the engine compartment).  My guess is you have a bad splice somewhere that is flakey.

When you first stated it wouldn't start sitting overnight, my first thought was a bad battery.  It still could be that, but you say the starter does crank.  Check to see what the voltage is at the battery while cranking.  If it drops much below 10.5V, you won't be able to start the car.

Thanks midlife, I will have them check all this out.

run_horse Run Horse Run!
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