Spark question

[Subarmale]

After 2 years of restoration my ‘71 Bronco Sport if finally running. Except for a couple of electrical issues it seems to be running pretty well. I’m still trouble shooting a gauge problem but my first priority is figuring out why I have no spark when I crank the engine. It won’t fire while I’m cranking but as soon as I release the key to the On position it starts to get spark and usually still has enough RPM from cranking to fire the engine. Anyone have some basic trouble shooting tips or ideas on where to start looking?

 

[DirtDonk]

That’s an interesting dilemma. Obviously your engine is tuned very well, or it probably wouldn’t get that little bit of life after you release the key. Good job on that.
There are a couple of things that can cause this. Primarily though, the ignition switch is a known trouble point where if you turn it too far to the start position, it will cut off the other circuits.
Both the red with green stripe wire to the ignition coil and the green with red stripe wire to this voltage regulator are supposed to stay energized when the key is in the start position.
Right now it sounds like they are not.

You can try a couple experiments first. See if you are turning the key too far by just barely turning it and when it starts to crank keep it there don’t go any farther.
The other experiment is to see why the starter relay is not doing its job.
Is this a new wiring harness? Or original? If original, remove the brown wire from the “I” post on the starter relay/solenoid, and apply 12 V to it.
You can run a jumper wire directly from the battery positive to the brown wire. Just don’t leave it there for longer than it takes to run this test.
Once you have power to the Brown wire, immediately go in and turn the key to start and see if it works normally.
If it does, you have a defective starter relay.
And maybe a defective ignition switch too!

 

[73azbronco]

What he said^^ and make sure wiring is correct on starter switch.

Disco battery, use an ohmeter touching coil terminal and unhooked battery cable positive side, in start and run positions to see if its connecting.

How old is starter switch? Fun fact, I went through four "new " ones before I said no way, and I have the oem 1973 switch in now, works great.

 

[B RON CO]

Hi, you can check the I terminal on the solenoid with a test light. Remove the wire and have a helper turn the key to start, or use a remote starter switch. The I post should be hot when the starter is spinning, and off when the starter is not spinning. The I post feeds 12 volts to the coil when the key is turned to start. If the I post is working correctly, follow the wire, it may not be hooked up. Good luck

 

[Steve83]

For us to help, it's critical for us to know exactly how you "restored" it. Does it still have a complete unmolested undamaged '71B harness? Or has ANY change been made? We need the details. And we need to review them every time you post because we look at many others here as well as our own, so we won't remember yours from one view to the next, and we don't always re-read the whole thread from the beginning. So you should put ALL your truck's details & history (as much as you know) into your signature(<-click that) so it shows with each post, as this page explains:

(click this text)


Phone apps don't always show signatures, so you may need to switch to a real browser in desktop mode on your phone, or just use a desktop/laptop computer. Put your location (nearest city) in your profile &/or signature, & upload an avatar of the truck. Not all its details are relevant to these issues, but you don't necessarily know which ones are relevant, so just put everything in now. The more pics you post (NOT in your sig) of the truck, engine, wiring, labels, & undercarriage, the more likely we can help you.

 

[Broncobowsher]

I-terminal on the solenoid is "spark in crank". If the I-terminal isn't hooked up, isn't wired correctly, or the solenoid has failed and has no power to the I-terminal in crank.
The ignition switch doesn't have a reliable (although some do) connection to the ignition while in crank.
Correct repair of the I-terminal on the solenoid to the ignition is the correct fix.