Here’s another idea. On cars of this vintage the starter relay performed two functions. Sending power to the starter motor with the key in “start”. And bypassing the resistor which powers the coil. This is to create an extra hot spark during starting.
A bad coil wouldn’t usually prevent cranking, but maybe something got mixed up in the wiring from the starter relay to the coil, so when the key is in start now it is shorting something out, and all that current going to ground is preventing adequate current flow to the starter motor.
Get out your wiring diagram – on this car it is probably only 3 or 4 pages, unlike today’s cars where the wiring diagram can be 30 or 40 pages or more – and double check that the wiring from the starter relay to the coil is correct, and that the coil is correctly hooked up. I’d probably just disconnect both wires from the starter relay to the coil. One has a mark “r” on it, and the other “s” I think, marks on the starter relay case. If it cranks ok then, you’ll know there’s something wrong with those other two wires.
Just one more thing. Take a look at the negative battery cable. If the rubber is cracked anywhere along its length, change it. It also has a self tapping screw with a bolt head holding it to the fender about eight inches away from the battery. If that area is rusted, remove the screw and wire brush or scrape the area. That sounds unimportant but the problem can plague you forever if not fixed.
Thank you to everyone who gave their insight/advice and experience to help me with the no start issue! I wanted to let you know that I’ve finally got it resolved.
Today was the first day I’ve had real time to spend hunting down the problem since, Wednesday? Because many of you agreed (more or less) that it sounded like a bad connection, and I knew I had some wires that were about done, I spent about 4 hours today re-wiring the engine from fire wall to engine gauges. I also checked the other wiring including the alt, battery and starter. Gave them all a little tweak to tighten them, although none seemed particularly loose.
The problem turned out to be the NSS or Neutral Safety Switch connection on the firewall. On my mustang the plug was on the firewall spliced into the gauge harness. (the car was originally a manual trans and didn’t come with the NSS) Upon closer look, the plug was caked with dirt and the wires that lead down to the tranny had spots of melted tape, insulation and corrosion. I believe that when I was working on the engine I moved or nudged that harness and it was probably just enough to crack or break one of the frail wire connections. I fixed it by cutting out the bad section and the plug, got a generic $2 2-prong plug at parts store, cut it in half and spliced one end to the wires leading to the tranny switch and the other end I spliced into new wiring coming out of new firewall plug. Taped it up tight and ran new loom over it then headed for the key. I gave it a light turn to see if I had a click or crank and sure enough I got a crank. Within a few more minutes my baby was warming up! (btw my car body is a 64 1/2 w/o reverse lights, so I only needed a 2 wire connection rather than normal 4)
It seem like the 3 part cooling system flush and new 180* therm are working well too. The car never got over 2/3 hot even though it was just running in the driveway, unheard of before! After shutting it off it would start right back up with one key turn…I used to have to fight her to get her to start up again when she was already warm. (quite embarrassing at places like the gas station or a drive through)
Well I hope this resolution and the advice of everyone who posted helps someone else…old posts have really helped me in the past. This is the best DIY car forum I’ve ever been on!
Thanks for posting the solution, @Dani1966. This could help others with the same problem. I hope you come back and participate on a regular basis. You are always welcome here.
Glad you got it fixed and thanks for the update. So many vehicle problems are caused by just simple wire connection issues, especially at the battery.
There are a lot of good sharp regular members here that give out good free advice. Now that you have the wiring problems fixed you can put a good polish on that nice classic you have there.
I agree with the suspicion of the battery. Checking the voltages before and during cranking will be useful.
Also, check the voltage drop across the starter solenoid during cranking (or, since there is no cranking, while you have the key turned to “start”). The contact plates in that solenoid have been known to get corroded over time, which impedes the current flow to the starter.
OMG! What a great car! Glad you have her running smoothly and back on the road again. Good for you for fixing it.
Edit: One thing that confused me was that were were hearing a click with the key in “start”. I wouldn’t have expected that if the problem was the NSS. The NSS broke on my 70’s Ford truck and it didn’t click. But if the switch was ok and the connection to it developed a high resistance, then that click symptom could happen.