Dead mustang, will not turn over.

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Jan 19, 2022
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My Car
1971 Mach 1
Last Saturday I tried starting my 1971 Mach 1, have 351c with automatic trans.

Turned the key, nothing usually I can hear the fuel pump for the fi-tech carb.

The headlights came on, interior dome lights too. But nothing, I tried moving the shifter to make sure it was in park, nothing. Even tried in neutral, nothing.

Checked the battery and starter solenoid connections all good, still would not start.

Luckily my mechanic was open so I towed mustang to the shop. While unloading he got inside, tried starting and it started right up… really???

They checked it out and said it was bad connection at starter solenoid, started it up a few times during the week, no problems. Drove it home Friday night, no problems. Tried to start Saturday morning… nothing again. Dead!!!

Now I’m thinking it may be the neutral safety switch. Would a bad switch not allow the fuel pump to engage?

Any help would be appreciate, thanks
The neutral safety switch just functions when the key is in the start position, and has nothing to do with the fuel pump, which is wired into a key on hot circuit.
I would check the condition of the connectors at the starter solenoid, including the battery cable, and make sure they are properly crimped to the wires. I prefer to solder the connections on critical connection like these. The battery terminals and connections may also be corroded. The grounds may also be bad, very common issue.
One connection I would check if you haven’t done so is the cable from the solenoid to the starter. I’ve had a similar issue in the past and I found the cable connection at the starter which seemed tight was loose enough to not make a good connection.
If you try moving the gear selection from Park to Neutral and try to crank it again you may get lucky with a Neutral Safety Switch (NSS) with its contacts in the Park position no longer carrying the current needed to let the Starter Relay (aka Solenoid) activate and crank the engine over. But, a failing NSS ought not be involved with the circuit for an electric fuel pump, so that is a mystery. Another possibility is the ground cable/strap between the engine block and the shell of the vehicle may not be allowing enough current to flow when you try to crank the engine over. And, of course, there is also a possibility the ignition switch (the electrical part, not the ignition key lock and tumbler assembly, may be causing the issue.

It is a shame the problem could not be duplicated at the repair ship. These intermittent issues can turn into real nightmares. That said, when I see unusual and especially intermittent problems, more often than not it is due to a bad ground. And, do not let ground connections that "look good" fool you. Just last year the electric fans on out 73 Mustang Convertible failed to turn on, and the engine overheated. When I got home I began to diagnose the problem almost accidentally by bumping the ground connection while I was preparing to perform the diagnosis. The ground connection looked fine, but I verified the ground connection is precisely where the problem was - despite the ground lug being connected tights to the radiator support bracket. I was having Lynda video record the diagnostic process so i could post it to YouTube. As it turned out it is an especially worthwhile video as it shows how a bad ground can exist even if the ground connection looks good.

You know, another cause could be due to the started brushes not making a good contact to the armature contacts, or the copper disc inside the Starter Relay is no longer able to carry the current needed to let the starter motor engage (I have seen both happen). To test for that the next time the ignition key does not let you crank the engine, and shifting from Park to Neutral does not work, short the terminals on the large positive terminal on the Starter Relay to the Relay's "S" Terminal. You should at least heard a solid "click" as the copper disc inside the Start Relay is connecting the two large terminals that feeds the started motor. If you hear a solid click, but have no cranking either the brushes in the Starter Motor are worn out, or the contact disc inside the Starter Relay are too arced and damaged to carry enough current to let the starter turn over. And, it could still be a bad ground.

The YouTube video I mentioned above is at:

It is at 04:11 into the video that I accidentally nudge the failed ground and cause the fans to com eon. I recognized what happened pretty quickly, but kept moving forward with my diagnostic process just to show how I normally attack those kinds of problems. Then, at at 05:50 I get into the cause of the open circuit problem. Now, I know the video involves electric cooling fans not working, vs your starter not working. The point I want to share is that bad grounds do cause problems, even if they look fine.

That is a lot to dump on you. Please post updates re: the problem still happening after you do some more testing, or if it was resolved.
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I would be willing to bet the starter solenoid is the culprit here, mostly because the shop that looked at it said it was a bad connection at the starter solenoid. Starter solenoids on Fords are like the Mopar electronic ignition control units and their ballast resistors, you should always have one in your glove box, especially now, with all the China garbage that is coming in. I would go to your local NAPA and get their heavy duty starter solenoid, they sell 2 of them, do not buy the cheap one as it is junk. See if they have both of them and ask to see them both, the HD one seems to weigh twice as much as the cheap one, it has that much more windings in it. The good one is made by Echlin, and comes in a NAPA box. It is here:
And if it comes out that the culprit was not the starter solenoid, you now have a spare in your glove box. eventually, you will need one.
On the starter Solenoid there are two small posts. The one closest to the battery gets power when you turn the key to the 'crank' or 'start' position. A simple test is to take a piece of wire and attach it to this post, touch the other end of the wire to the positive battery post. Do this with the key out of the ignition to make sure the car doesn't start (removing the main coil wire is a bit of extra insurance). The engine should crank. If it does, your problem is with the key, safety switch or some other part of the circuit. If it doesn't crank you are probably looking at a bad solenoid.
Sounds to me like you may have an ignition switch issue or connection.
With the key on, the fuel pump should charge the system and you should have power to the coil. Check your ignition switch, make sure it hasn’t come loose.