'77 C4 - Won't Start

[techfab]

Hi All,

I need some help.
As stated, '77 original 302, C4 all original. wiring. Been running like a peach for years. Drive her almost daily. Tried to take it to the golf course yesterday and wouldn't fire (after running fine the night before). I have read through all of the related posts here that I could find. Here is what I have done so far:

- Key on and all electrical works.
- Turn key to start and only get a very faint click (not from start relay).
- Tested power at wire attached to "I" on relay and get 9 volts when in run.
- Tested power at wire attached to "A" and get nothing when ignition turned to start
- Put in neutral and Jumped from bat positive to "A" and fires right up (scared the crap out of me with how easy it started).
- Tried bypassing the NSS by disconnecting and jumping between the 2 red/blue wires - had no effect.

This is about as far as my research on this site has taken me. Not sure what to test next.
I really thought it would be the NSS as a very few times over the past 4 years of ownership when an attempted start acted identical I jiggled the shift selector in park and it fired. up.

Any thoughts on what to test next? Thanks in advance for any help.

 

[DirtDonk]

I bet it was a startle when it cranked! Yes, many have said the same thing so we're all glad here that you put it in neutral first! Or park of course.

Check one more thing. It's leading to the ignition switch, but check anyway.
With the NSS connector separated, check for voltage on BOTH of the Red w/blue wires with the key in the START position. This is done only on the body side, as the transmission side would have no power once the switch is disconnected.
Reason for this test is that you already did the jumper test and it did not work. If the jumper wire was set correctly and you have voltage on the circuit, it should have cranked the starter. Since it did not, I suspect that it's not getting there from the key.
If you do find power on one of the wires (you're testing both because I don't know which one is hot and which one is load) then the ignition switch is doing it's job. If not, then likely the switch is bad.
You can test that too however, because it's always possible for the wires to have gone bad.

Speaking of testing the switch, that might be even easier than testing under the hood. Just put your voltage probe into the connector where the Red w/blue wire comes out of the back of the ignition switch and hope for no joy. You should see 12v (approx) at the connector, so if you don't, the switch is bad.

paul

 

[Slowleak]

Check for power at the red/blue wire, “S” at the starter relay, with the key switched to “start”. If you have no power then you have a bad NSS or ignition switch. Since you tried bypassing the NSS I would suspect the ignition switch. You can also test it on the back of the switch. The faint click you hear is probably the throttle solenoid at the carburetor.

 

[techfab]

I bet it was a startle when it cranked! Yes, many have said the same thing so we're all glad here that you put it in neutral first! Or park of course.

Check one more thing. It's leading to the ignition switch, but check anyway.
With the NSS connector separated, check for voltage on BOTH of the Red w/blue wires with the key in the START position. This is done only on the body side, as the transmission side would have no power once the switch is disconnected.
Reason for this test is that you already did the jumper test and it did not work. If the jumper wire was set correctly and you have voltage on the circuit, it should have cranked the starter. Since it did not, I suspect that it's not getting there from the key.
If you do find power on one of the wires (you're testing both because I don't know which one is hot and which one is load) then the ignition switch is doing it's job. If not, then likely the switch is bad.
You can test that too however, because it's always possible for the wires to have gone bad.

Speaking of testing the switch, that might be even easier than testing under the hood. Just put your voltage probe into the connector where the Red w/blue wire comes out of the back of the ignition switch and hope for no joy. You should see 12v (approx) at the connector, so if you don't, the switch is bad.

paul

 

[techfab]

DirtDonk, you are a god among men around these parts! Thank you for your reply.

I tested at the 4-wire connector (at firewall) and neither of the red/blue wires had power when in start. One of the black/blue wires had power when ignition on.

I then tested at the ignition switch and the switch appears to be working properly (power on the red/blue post.. I did see a questionable crimp connection and replaced that with soldered splice; but, no love.

I did notice that when I jumper the 2 black NSS wires the backup lights come on;; but, when I reconnect the cable, turn ignition on and shift to reverse they do not. Probably an unrelated issue; but, thought I would mention.

Are there any fuses between the ignition switch red/blue and the pigtail NSS connector inside the firewall?

 

[techfab]

Check for power at the red/blue wire, “S” at the starter relay, with the key switched to “start”. If you have no power then you have a bad NSS or ignition switch. Since you tried bypassing the NSS I would suspect the ignition switch. You can also test it on the back of the switch. The faint click you hear is probably the throttle solenoid at the carburetor.

Thank you.

No power at "A" when in start. I tested at the ignition switch and it has power on the post where the nss wire is connected when in start. Wondering about any fuses between ignition and nss?

Edit: sorry, does have power at "S"

 

[EPB72]

Thank you.

No power at "A" when in start. I tested at the ignition switch and it has power on the post where the nss wire is connected when in start. Wondering about any fuses between ignition and nss?

Edit: sorry, does have power at "S"

SeaBiscuit68

there would be no fuses

 

[Slowleak]

Thank you.

No power at "A" when in start. I tested at the ignition switch and it has power on the post where the nss wire is connected when in start. Wondering about any fuses between ignition and nss?

Edit: sorry, does have power at "S"

I’m not clear what you refer to as “A”. Is it “S” in the picture below? The brown wire connects to “I” and runs to the coil. The red/blue from the ignition switch connects to “S” which activates the solenoid/starter. There is no fuse between the ignition switch and the NSS. This pic shows the terminal labels and wire colors.

Sent from my iPad using Tapatalk

 

[techfab]

I’m not clear what you refer to as “A”. Is it “S” in the picture below? The brown wire connect to “I” and runs to the coil. The red/blue from the ignition switch connects to “S” which activates the solenoid/starter. There is no fuse between the ignition switch and the NSS. This pic shows the terminal labels and wire colors.

Sent from my iPad using Tapatalk

Thank you for the diagram. Very helpful.
Post "S" does not have power when in start (I thought I saw it referred to as "A" in a different image.) Per this diagram, the issue has to be the red/blue wire between the ignition switch and the NSS as the NSS has power at the back of the switch when in start; but does not at the firewall connector. Or, I guess it could be corrosion inside the connector. I will try cleaning the connector terminal and attempt another voltage reading before trying to trace down wiring. May just replace the pigtail.

 

[Slowleak]

Thank you for the diagram. Very helpful.
Post "S" does not have power when in start (I thought I saw it referred to as "A" in a different image.) Per this diagram, the issue has to be the red/blue wire between the ignition switch and the NSS as the NSS has power at the back of the switch when in start; but does not at the firewall connector. Or, I guess it could be corrosion inside the connector. I will try cleaning the connector terminal and attempt another voltage reading before trying to trace down wiring. May just replace the pigtail.

Sure sounds like it. Sometimes those old wires are broken inside the insulation. I think you are on to it. Good luck.

 

[Brush Hog]

I had the same problem on mine. It was a bad ground wire on the battery. It was barely hanging on. Would get some power but not enough to crank or start just a click from starter solenoid.

 

[DirtDonk]

Brush Hog brings up a good point. In spite of the fact that it does sound like you’re zeroing in on the problem, it wouldn’t hurt to verify and re-verify that your main battery ground cable between the battery and engine block is good, clean and tight.
It’s never a bad idea to cover the basics first while you’re chasing down a wiring gremlin

 

[techfab]

Brush Hog brings up a good point. In spite of the fact that it does sound like you’re zeroing in on the problem, it wouldn’t hurt to verify and re-verify that your main battery ground cable between the battery and engine block is good, clean and tight.
It’s never a bad idea to cover the basics first while you’re chasing down a wiring gremlin

That was it! It was the pigtail wire from the ignition to the NSS.
I have had the overall truck looked over by 2 different "Bronco Experts" and both said the wiring was original; but, looked remarkably solid. They both said they wouldn't recommend a rewire (even though that is part of their service).

On inspection, the wire I replaced looked good but definitely cracked inside the insulation aa it had no visible exterior issues.

I think it is time for the Painless (or Centech?) kit install. It just runs so well I really hate to mess with any of it; but, would be a fun father/son project. I did a '57 Chevy rewire 30 years ago. Kits must have gotten better since then.

Thank you all for your help.

 

[DirtDonk]

Congratulations! Not an easy find.
I have rewired Broncos because the original wiring had hardened weak outer jackets, but I wouldn’t necessarily do yours yet. But…

Knowing what you know now, I would look at all the connectors and wires that are easily accessible whether under the hood or under the dash and move them around, flex them, inspect them closely. If any others seem to be in the same condition as that one, then yes I would probably consider a rewire.
If the others seem pretty good, then no I would go with the fact that everything looks and works well and just drive it for a while.

 

[techfab]

Congratulations! Not an easy find.
I have rewired Broncos because the original wiring had hardened weak outer jackets, but I wouldn’t necessarily do yours yet. But…

Knowing what you know now, I would look at all the connectors and wires that are easily accessible whether under the hood or under the dash and move them around, flex them, inspect them closely. If any others seem to be in the same condition as that one, then yes I would probably consider a rewire.
If the others seem pretty good, then no I would go with the fact that everything looks and works well and just drive it for a while.

Will do. Thank you.

If we decide to rewire, I know you need to stay somewhat agnostic; but, is Painless the way to go these days?

 

[DirtDonk]

I actually like them all for various reasons, but Painless has by far and away the most reasons to like it other than cost.

 

[fluffybunny]

Another plus I got from using Painless is that when I ordered it from them, I gave them my Summit Racing account information so they placed the order through that, which got me some Summit bucks to use on other stuff.