70 Bronco Wont Start After Warm Up

[tonytony9]

That’s a good call to move the relay. And doing so will most likely necessitate at least some new battery cables.
Never hurts to renew, and upsize the battery and starter cables.

Some tests you can run, just in case it is still doing this when you get back on the road, driving it in the heat.
Carry some cool water with you and the next time it won’t start, dowse the starter relay. Give it a moment to cool, then try to start again. If that fixes the problem, then perhaps you need a more robust relay.
If that doesn’t fix it, then move on up the chain to see what else might be causing the issue.
Something between the ignition switch and relay. Perhaps one of the wires is compromised.
Follow the red with blue stripe wire as far as you can and see if it has any kinks, tears, cuts, or otherwise compromised points.

The water trick works like a charm. Thank you, this has helped me a few times in a pinch the last few days.

I am going to start with the relay and the cables. And continue down the line if necessary.

Can you clarify what you mean by a more robust relay? Are there specific relays you would recommend? I picked up a Motorcraft at the autoparts store for around $40.

 

[tonytony9]

Oh, and another thing…
Since you have a 70, that presumably has not been rewired(?) you need to go through and do some general maintenance that is not normally required on modern vehicles with modern connections and fuse panels.
Separate the two rectangular firewall connectors with all the wires coming and going, and make sure that all the connections are clean, tight and rust free.
Apply some dielectric grease and reinstall them.
Next go to the fuse panel and remove all five fuses. Clean them up, and reinstall them.
If the fuse contact points need cleaning, do that too as well.
Glass fuses build a crust of oxidation that, over time will reduce the ability of the electrons to pass through.

Awesome advice, yes, original wiring. I will do this today.

As a longer term project, I was considering buying a painless wire harness and redoing all the wiring. Yay or Nay for this idea?

 

[gr8scott]

Yay or Nay for this idea?

Yay all the way. New wiring is one of the best things you can do for your Bronco.

 

[m_m70]

As a longer term project, I was considering buying a painless wire harness and redoing all the wiring. Yay or Nay for this idea?

Yes

 

[DirtDonk]

The water trick works like a charm. Thank you, this has helped me a few times in a pinch the last few days.

Nice! Now you’ve narrowed it down and can move forward.

Can you clarify what you mean by a more robust relay? Are there specific relays you would recommend? I picked up a Motorcraft at the autoparts store for around $40.

As you suspected, I simply meant better quality. There’s some pretty cheap crap out there these days.
You may have done that already by choosing Motorcraft over the $10 no-name brand house brand specials. Many of those have lifetime warranties, but that warranty doesn’t do you any good when you’re stranded in the middle of nowhere, half a state away from the nearest store that can warranty it for you.

While it is possible that your relay started out wimpy, it’s also possible that it just got old earlier than it’s normal time, due to the heat.
For a specific brand, I happen to like the not very reasonably priced Volvo/Penta marine rated versions. They’re probably 80 or 90 bucks apiece by now. Maybe more!
But a Marine rating usually gives a part a little leg up on the competition in the longevity in the saddle department.

 

[73azbronco]

check the battery as well, low voltage can cause the relay to not work. How old is the battery? They are usually lasting less than 3 years, one is not unheard of.

 

[tonytony9]

Nice! Now you’ve narrowed it down and can move forward.

As you suspected, I simply meant better quality. There’s some pretty cheap crap out there these days.
You may have done that already by choosing Motorcraft over the $10 no-name brand house brand specials. Many of those have lifetime warranties, but that warranty doesn’t do you any good when you’re stranded in the middle of nowhere, half a state away from the nearest store that can warranty it for you.

While it is possible that your relay started out wimpy, it’s also possible that it just got old earlier than it’s normal time, due to the heat.
For a specific brand, I happen to like the not very reasonably priced Volvo/Penta marine rated versions. They’re probably 80 or 90 bucks apiece by now. Maybe more!
But a Marine rating usually gives a part a little leg up on the competition in the longevity in the saddle department.

I like the idea of the Marine rated, those motors run hot and hard. Plus the water proofing is to my liking. I had already purchased my relay, which I am now realizing I misspoke; it is a Duralast. Any complaints here?

Also, is it accurate that when I relocate this to front side of the wheel well I will have to scuff up the paint for the mounting surface. I was told the bracket is a grounding point. I would prefer to not create another area of rust is there a way to avoid this?

 

[tonytony9]

check the battery as well, low voltage can cause the relay to not work. How old is the battery? They are usually lasting less than 3 years, one is not unheard of.

I don't believe this is the issue this time around, although, something to check either way as the battery is from PO

 

[m_m70]

Also, is it accurate that when I relocate this to front side of the wheel well I will have to scuff up the paint for the mounting surface. I was told the bracket is a grounding point. I would prefer to not create another area of rust is there a way to avoid this?

You could run a wire with ring terminals from the bracket to a known ground or to the battery.

 

[DirtDonk]

Even Ford didn’t go overboard on grounding. They just stamped the holes and ran screws up.
Of course, back then the metal was pristine, and a good ground connection. But you can just make sure your holes are clean after you thread the screws in, AND do what was suggested and add the body ground right there to your mounting screw.
The original battery cable had the ground connection to the inner wheel well, just below the starter relays position.
You can put your new, renewed ground to one of the screws with the ring terminal as suggested. Win win!

 

[DirtDonk]

And as always, if you connect something to the body, I typically do scuff the paint underneath the connection, then spray a spritz of closely matching paint right over the screw.
Keeps rust at bay, and even though you can see it, it looks very purposeful and well thought out.

 

[DirtDonk]

it is a Duralast. Any complaints here?

I don’t wanna spread vicious rumors, but I think those are one of the more poorly thought of brands. Many of them work just fine, but far too many of them fail quickly.
I’ll have to go back and look at the thread on another forum that is dedicated to tracking and tracing bad Ford starter relays. Listing manufacturer model number, where and when it was bought, how many warranties it took to get a good one finally, how long before it failed, or if it was bad right out of the box.

In other words, non-factory original Ford starter relays are quite notorious for being highly failure prone among new parts.
There are multiple instances people getting two, three, and even four bad parts in a row.
This includes Ford starter relays at the top of the list, but does not exclude voltage regulators, ignition control modules, points and especially condensers, and Dura spark distributor reluctor/stator kits.

It’s a scary world out there!

 

[73azbronco]

I use duralast in all my rides, platinum of course. it fails in two years, i get a free one for another 2 years, getting 4 years for the price of one. and autozone is on every corner in America.

What has not worked? Optima, I have the special $200 plus charger, and they still only last 2 years, with zero warranty.

Best I have seen, ford batteries, max, son has one at 6 year point in Phoenix heat.

 

[Speedrdr]

Best I have seen, ford batteries, max, son has one at 6 year point in Phoenix heat.

The battery that came in my ‘13 F-150 was replaced either December of ‘23 or January of ‘24. Can’t get much better.

Randy

 

[gr8scott]

Starter Solenoid-Relay Motorcraft SW-7663 for sale online | eBay

Find many great new & used options and get the best deals for Starter Solenoid-Relay Motorcraft SW-7663 at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[m_m70]

Best I have seen, ford batteries, max, son has one at 6 year point in Phoenix heat.

Got 11 years out of my NAPA legend
(East Penn MFG).

Happy with that.....

 

[tonytony9]

Thought I would shoot over a follow up/close off this thread.

Replaced and relocated the starter. Did a little wire clean up. Put a decent amount of miles on it since, no issues with starting! Thank you all for the advice.

 

[DirtDonk]

Looks great. Took Ford four model years to figure out that (even back then, when parts were of much higher quality) even starter relays don’t do their best work when hot.
Probably already knew that, but the design was wrapped around the six cylinder engine originally. Much different heat dynamic under the hood.