No power. No nothing. Out of ideas.

[ebbronco]

thanks 73azbronco. I replaced the battery to block ground just in case. I don't know/can't find other grounds on the truck. I mean, isn't the battery to block ground the receiver for the current travelling through the chasis, etc.? Do these early Broncos have grounds that i'm unaware of?

 

[jamesroney]

Don’t be sorry. You’re getting close.

You said that you had no headlights, and no ignition...but you do have power to the fuse box. So If you look at the wiring diagram, you have battery power on circuit #37, BK/Y. Look at splice location S-204. That’s the only place where you can lose power to the headlights, and ignition...but still have power to the alternator and the fuse box. S-204 is where the #37 BK/Y (there are three) and the #21 Yellow, and the #25 Black/Orange all come together. It looks far apart in the diagram, but it is really pretty near to each other in the harness.

Measure the voltage at the yellow wire at the ignition switch, and at the headlight switch and at the ammeter, and then you will know where you lost power.

Good luck!

 

[DirtDonk]

Okay, I don't see a fusible link on the truck. It's a '73 so based on what ya'll have told me, it probably just has the one near the starter solenoid. It's not there.

Then things have been changed and it's been cut out. Does it look like this has happened? Please by all means take some good pics.
To post pics directly you have to become a contributor for 12 bucks a year. But you can also upload them for free to your "Garage" and "Gallery" functions in the UserCP above.
In a pinch you can also e-mail them to me at paulb@aol.com and I'll post them for you.

As Dirtdonk said, the black and yellow/black wire combination forms a loop that is responsible for all power. I have 12 volts at the black and yellow wire on the back of the alternator and 12 volts at the solenoid where the black wire lands. How could I have 12 volts at the alternator if the black wire/black and yellow wire combination was open?

AND, I have 12 volts at the fusebox, too.

As I mentioned before, the volt-meter uses almost no current to measure voltage. So you could have literally one fraction of one single strand of the inner conductor still connected and you will see 12v at both ends of that wire. What can't happen however is it being able to pass enough current to even light up a small light bulb. This could give a false sense of a complete circuit.
Perhaps a voltage drop test would be appropriate here? Maybe someone can 'splain that to us so you could test my theory?
Or perhaps I'm wrong and if that single strand was all that was intact you would already see a significantly lower voltage at the alternator. Maybe someone can explain if my half-blown fusible link theory is even valid.
If it's not I can't see how you can read 12v at the fuse panel yet nothing works when you turn on the switches.

What's eating on me is something Dirtdonk said about the ammeter...that if it were disconnected the truck would be dead. I see where the two wires connect on the back of the instrument cluster, but not that they feed the ammeter.

The wire passes through an inductive loop on the back of the gauge. There is no direct connection to the gauge other than this loop. It may appear as only a simple retaining device, but it is in fact the actual sensor part of the instrument.
If you have separated the two halves of this connector and are still seeing voltage readings everywhere you did before, then you are not reading it right or your instrument is not working properly, OR it's just a partial connection but enough to read some voltage.
With the two halves separated, there should be power only on one half of the wire. The half that goes back to the battery.
At that point however, you should for sure read ZERO volts at the back of the alternator. With the wire completely disconnected from the battery, there is no other possible reading.

I replaced the battery to block ground just in case.

Not that this would cause your problem, but where exactly did you connect to the engine block?
Just curious, but more on grounds in a minute...

I don't know/can't find other grounds on the truck. I mean, isn't the battery to block ground the receiver for the current travelling through the chasis, etc.? Do these early Broncos have grounds that i'm unaware of?

Yes they do. And no, it's not enough to use just the engine block.
Remember the engine is rubber mounted. Some does manage to pass through various points where metal touches metal, but it's a very inefficient ground path.
Ford left the Bronco out in the cold when it came to grounding, but at least they did include one more main ground contact area. Directly to the body at the wheel well. If you look you will find a nice punched screw hole facing the exhaust manifold on the passenger side near the front crease/fold of the wheel well. This is where the original ground cable attached to the body before it reached the engine. If you were the one that replaced the factory original, it might have appeared to be a simple clamp to hold the cable in place. But it was in fact connected internally and acted as the body ground.

Even though this does not usually kill all the power to have that ground missing, it certainly does not help the situation. So adding a few of your own is a good thing and is a long standing practice that we preach here to anyone doing wiring work on their Bronco.
You'll need some length of 10ga wire (Black preferred naturally) so you can make at least two of your own. One from the battery negative down to the wheel well, or fender apron area. Many of us run it to one of the bolts holding the starter relay in place. Just about anywhere is good.
The second ground that comes in very handy is what all modern cars have and even Ford full-size trucks had them while Broncos got left out. That's running one from the back of the intake manifold or block-to-bellhousing bolt to the firewall. Either to an existing fastener on the firewall, or a newly created one by you.
This was not absolutely necessary when the bodies were brand new, but after 50 years or so of rust and paint the connection between all the body panels has gone soft. So just attaching the one to the wheel well is not always best for dash mounted accessories and switches. In other words your radio will thank you if you add that second ground.;D

Paul

 

[ransil]

get a voltmeter and start troubleshooting, troubleguessing only gets parts thrown at it.

 

[ebbronco]

Dirtdonk and Jamesroney, I really appreciate the time you've given to this. I'm going to try to actually test the suggestions.

I can't believe that I'm at this point. The Bronco was spinning like a top with the new distributor and I mucked it up by not tightening ONE nut. I'm missing out on the best weather of the year for a bikini top. Uggghhh.

I must have been one bad dude in my previous life.

 

[SP73]

OK I had this same issue on a tacoma, battery was not secure and positive grounded to hood over a speed bump. Melted every ground fuseable link on the truck, 4 of them to be precise. Luckily, because of the the links nothing was damaged. Odd part was it really did not make logical sense because I thought the juice would go from hood, to body, to block, to battery, but took three other routes back as well, that is your issue.

What you need to check is continuity to all the grounds, it may have melted your ground wires somewhere along the way. Oddly it probably did not melt the battery ground wire but who knows. Think of it this way, when the hot grounded to body, all the grounds became hot, trying to find a route back to the battery.

^^^This is where I’d be looking also. I’ve had it happen twice on my dump trucks. The second time it happened to my truck, I could start it and it would run (zero lights or accessories), but it wouldn’t shut off. Bad/burnt grounds make for strange behavior!

 

[ebbronco]

I'm definitely looking into that.

 

[EPB72]

As I mentioned before, the volt-meter uses almost no current to measure voltage. So you could have literally one fraction of one single strand of the inner conductor still connected and you will see 12v at both ends of that wire. What can't happen however is it being able to pass enough current to even light up a small light bulb. This could give a false sense of a complete circuit.
Perhaps a voltage drop test would be appropriate here? Maybe someone can 'splain that to us so you could test my theory?
Or perhaps I'm wrong and if that single strand was all that was intact you would already see a significantly lower voltage at the alternator. Maybe someone can explain if my half-blown fusible link theory is even valid.
If it's not I can't see how you can read 12v at the fuse panel yet nothing works when you turn on the switches.

dirtdonks comment is correct ..using a voltmeter puts no load on a circuit ,,,atest light would put a load on a circuit old school test lights draw about 300 milliamps,,..I've made my own test lights using a high/low beam headlight both high/low wired together and then the ground make leads as long as you want and whatever ends you want it's a great tool for testing and loading a circuit.

If only using a meter then a voltage drop test is best but can lead to a little confusion if not sure what your doing..

so retest with a light that will load the circuit ...

and Yes fuse links can burn and still have contact and show voltage on the back side but loose it when loaded ..seen it had a econoline came from two shops {one was the dealer| van had new computer ,distibutor , module, co-worker was struggling with it but on the right track ..short story fuse link..seen fuses blow where the melted metal wedged between the contacts as well..

 

[73azbronco]

Im wicked good at weird stuff like this wish I was there to help. Try looking at one of the side running light bulbs on body, see if it is fried?

 

[71 CA Bronco]

Where are you located? Maybe someone can stop by and help trouble shoot.

 

[ebbronco]

73azbronco, why do you ask that? Are you saying that that may have been one of the possible paths of the current?

Man, I wish that were possible. I live in Ethel, Louisiana, which is about 30 miles north of Baton Rouge. I think i'm out of range.

It may take a while, but I'm going to find out what the deal is, mostly because of this forum. I've never run across a short resulting in something so serious. Ya'll wont here about it for a while, as I have to work and these short days limit what I can do. No garage. Just the yard. HaHa.

 

[Rustytruck]

make sure you have a ground wire from the negative pole of the battery to the body make sure the ground cable on the engine block under the alternator is clean and tight. make sure the mounting bolts under the starter solenoid and the voltage relay at the fire wall are clean and tight. these grounds are extremely important. if your battery is truly 12.1 volts you have a dead battery battery gets over voltage on charge up to 14 volts turn off the charge and let the battery sit over night. battery will be 12.7 volts on a good battery 12.5 volts as the battery ages when the battery gets down to the 12.2 range most cars wont start any more, new model cars have a low voltage cutoff at low voltage to protect very sensitive electronics

Get your battery charged. if you lost your positive cable from the battery and it grounded that's a dead short when your alternator is at full charge that can cause allot of damage. on my Bronco there is a wiring connection coupler in the power line to the dash. its about 6 inches before the firewall engine side. not all broncos have it follow the wire bundle up from the solenoid towards the fire wall. this is the first connection after the fuse-able link so if no power there you know its the connection at the solenoid is the problem. Fuse-able links can fail with no outward signs so it looks good doesnt apply.

 

[JSBX]

Check the bullet connector behind the ammeter. I did something similar and the bullet connector burnt causing the same problem.

 

[ebbronco]

Just an update. I replaced the black/red---black/yellow main power loop with 10 gauge primary wire with little result. There is some action at the turn indicators and horn. When I turn the indicator left OR right, they both blink as though the hazards are on AND the instrument cluster lights blink in unison with the indicator. Also, when I press the horn button, the lights on the dash illuminate. HaHaHa...almost there.

I realize that my limited skills are hindering the resolution of all of this.

Rustytruck, thanks for the suggestions. I'm going to ground the doo-doo out the bronco as you've suggested and then go from there.

I took a crash course in using an ammeter and practiced with small batteries to get a feel for it, but I can't get ANY readings in the truck. The study of all of this goes on.

 

[ebbronco]

It was the grounds! It was the grounds! It was the grounds!

 

[Rustytruck]

its almost always the grounds. make sure you clean and tighten all the grounds I listed.

 

[ebbronco]

Thanks Rustytruck. I did exactly as you said. I removed starter solenoid and regulator...cleaned and sanded all mount surfaces, ran a ground from negative battery post to firewall, and cleaned and sanded grounds I could find that terminated on the body. Not thinking that that could actually be the solution, I hooked everything up to begin trouble shooting, turned the key to the on position just or kicks, and EVERYTHING came to life.

THANKS TO ALL FOR YOUR INPUT. THIS WAS A GREAT LEARNING EXPERIENCE FOR ME.

Can't wait to break down again.