1972 Bronco No Crank

[BroncoClubofAm]

I have a bone stock 72' with a 302 manual trans. After sitting for two weeks it would not crank, nothing. No click, no noise. Headlights and heater fan work. So far I've done the following to no avail:
- tested battery 12.4V
- replaced solenoid twice (thought I got a bad one, upgraded to higher grade)
- R&R starter and had it bench tested, it passed. Eventually tried a new starter as parts employee inspired little confidence. Both starters passed my test on garage floor connecting jumper cables.
- replaced cable from solenoid to starter
- Inspected and cleaned negative cable on battery side and at the block
- Removed starter side wire at solenoid, tested by cycling ignition. When moving key to starting position it reads 12.4V then goes back to 0 when key is off. Tested numerous times and it reads 12V or better each cycle.
- If you bypass the solenoid it will crank and turn over. Maybe I wasn't using a high enough gauge wire but it got hot and started fusing to the solenoid.
- If you put a wire to the positive cable and then touch the "S" side of the solenoid, it will NOT crank.


I'm stumped. Any help would be appreciated.

 

[jmhend]

I wonder if you can use a screw driver and jump across the starter solenoid?

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[67sport]

Is the solenoid mounted to a clean (bare meta) part of the truck? It grounds the field circuit through the case, so it matters that there is good electrical contact between the case and battery negative.

Add a jumper from the solenoid case to the battery negative, and the try your key on start again.

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[BroncoClubofAm]

Thank you so much! I put the jump wire as you recommended and it cranked! Not sure why it worked before but regardless I'm so pumped. I've got 8 hours in this and now the end is in sight. Thanks again!

 

[67sport]

Good to hear. Grounding is as important as the 'power side of the circuit. There are almost as many right ways to achieve this as there are guys on this board, but - you should have a good ground cable from battery negative to engine block (near starter), a good ground cable or braid from block to frame, and block to body. If you have computers installed (efi) the grounding is even more critical. You can buy braided ground straps at marine stores or most auto parts stores that look good and work well to pick up the body in a few places.

Starter solenoid, horn solenoid , voltage regulator and a few others all ground through their case, so clean metal, and good tight fasteners will all help.

Good luck.



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[DirtDonk]

- replaced solenoid twice (thought I got a bad one, upgraded to higher grade)

Did you keep the old one? Now that you know there is a good chance it was working and just not getting a good connection, it'll make a good spare.

- R&R starter and had it bench tested, it passed.

For the next time ('cause there will most likely be a next time!), with no click, you can be fairly confident it's not the starter itself, but something before that.

- Inspected and cleaned negative cable on battery side and at the block.

That was a good call. But is there still a good ground wire from there to the body? There might be now that you've got things sorted, but what about before? Any body ground?
Originally Ford used the same single cable to connect both to the engine (of course) and to the body sheet metal at the wheel well. Lots of these get removed and ignored when changing battery cables, so it's good to get the type with an extra 10ga "pigtail" coming out of the battery lug.
If yours didn't have this, and you have not already, connect a new additional ground wire to the body. And it just happens that one of the screws fastening the starter relay/solenoid to the body is a great grounding point!

- If you bypass the solenoid it will crank and turn over. Maybe I wasn't using a high enough gauge wire but it got hot and started fusing to the solenoid.

Yep, you need a heavy gauge wire or other heavy tool to bypass the relay completely. You're literally passing the full current that it takes to spin the starter and turn the engine over through that connection. With an older starter, that could be 200 amps!
Which is why to do that jumper test you use either legit jumper cables, or as mentioned the handles of a pair of pliers, or other heavy metal object.
And even then, they can still get hot from passing all that current. Especially pliers since they have that gap that might not be tight, between the two halves.

- If you put a wire to the positive cable and then touch the "S" side of the solenoid, it will NOT crank.

Great testing. Sorry you didn't find this out before the hassle and expense (at least temporarily) of the new relays and starters. But whenever you can crank the starter by bypassing the relay, but it won't energize and crank when using the "S" terminal, then your problem is right there at the relay itself.
As you found out, it's either a defective relay, or the ground connection to the body is not good enough.

Sounds like yours was lack of a body ground more than a bad connection though. Just guessing that, because after replacing the relay multiple times the connection at the screw's threads should have been more than sufficient.
Are the holes rusty?

At any rate, keep those grounds coming! A good one from the battery to the body, and from the engine to the body at the firewall are great additions.

Paul

 

[jmhend]

Thank you so much! I put the jump wire as you recommended and it cranked! Not sure why it worked before but regardless I'm so pumped. I've got 8 hours in this and now the end is in sight. Thanks again!

Congratulations... its the little stuff that will kill your motivation. Stick with it. As Paul mentioned i would go over every ground. Then go over them again. Trust me I have endless hours in wiring troubleshooting and 7-10 times its a ground issue somewhere.

Grounds are killers when trying to troubleshoot.

Jason

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[BroncoClubofAm]

Thanks again! I had removed the engine and cleaned and repainted the engine bay last summer. I believe the repainting of the motor and fender wells also disrupted the ground at the engine and solenoid. I noticed when removing the new solenoid that the bolts holding them to the fender had copper washers that were dirty. Not only did it fix the problem but the starter and gauges are all working much better. On to the cosmetics. I've had 13 Bronco's and have 4 now and the biggest headaches have been electrical. Merry Christmas!