Amp gauge and voltage fluctuation? What needs replacing?

[fordfan]

I think this a fairly common problem on Broncos with the original wiring and amp gauge. I have at least two Broncos that do this. The amp hand wiggles so fast back and forth that it's a blur and u can't really read it. It wiggles from maybe -20 to +20 more or less. For a while, I kinda ignored it, but I've noticed on one that at idle with the lights on that you can actually see the lights vary in brightness with the fast surging of the voltage. I have checked it with a meter, but that was useless because it varies so fast. The alternator is charging, its just "quivering".

I've changed alternators several times, grounded the alternator and voltage regulator, changed regulator, installed new amp gauge, new alternator wiring harness, checked connections but it still does it. There is a fuseable link in one of the wires I think... Could this be it?

Help....help.... Viperwolf1? or Dirtdonk....or..... has anyone else had this issue and fixed it ?

Thanks!

 

[Broncobowsher]

90A 3G did wonders for me.

If staying stock, electronic regulator. Make sure the regulator has a really good ground to the battery as does the alternator. Make sure the sense wire has a real good connection to the positive battery.

 

[66BlueGoose]

90A 3G did wonders for me.

If staying stock, electronic regulator. Make sure the regulator has a really good ground to the battery as does the alternator. Make sure the sense wire has a real good connection to the positive battery.

What he said!

 

[DirtDonk]

I can't imagine that the gauge itself can have anything to do with the issue. It's totally passive and just has an inductive pickup that the wire passes through. Can't think of any way this instrument could change one thing about the actual charging system.

Usually the fusible links don't fail like that, but I don't think it's impossible either, since deteriorating wiring can do this.
You said you replace the alternator and regulator several times. How many? I don't like to even contemplate this, but it's a fact that many have gone through several defective parts right out of the box. So it can happen.
But to have the exact same issue with more than one? That's getting to the realm of a long-shot even with today's crappy parts.

Sounds to me like the wiring is deteriorating in multiple spots, perhaps at the regulator.
But first, where are your grounds? Main ground cable is directly to the engine block (not a bracket) and the main body ground is to the fender/wheel well area from the battery directly? Then at least one additional ground that you've added yourself between the engine and the firewall?
I don't remember a grounding issue ever being the ultimate reason for this oscillating output from the alternator, but have sure seen lack of proper grounding cause all sorts of other issues.

Have any buddies with older Fords nearby? Maybe the trick would be to temporarily swap in some known good working parts to see if you still have the issue.
What year is your Bronco? A '66 through '70 by any chance? Might simply be time to clean and tighten all connections, especially at the two rectangular firewall plugs.
If yours is a '71 or later then this does not apply.

Got pics of the engine compartment just in case we can see anything?
Regarding that fusible link, it won't hurt anything to disconnect the battery, then remove all the wires from the starter relay, remove the relay from the body, sand/scrape/brush the contact points where it mounts to the body, then do the same thing to all the ring terminals before you put them back on.

They build up a crust of corrosion that can wreak havoc on electrons sometimes.
Worth cleaning the stuff up even if it does not fix things right away.
But you have to start somewhere.

Good luck.

Paul

 

[fordfan]

Thanks! It looks like I have an examination due.

For the year models, one is a '69, one is a '71, one is a '72, and one is a '76 that all have these oscillating charges from the alternator. The '72 is the main one I have really tried to trouble shoot and it is 'Rattler'. I can post up photos of the wiring near the alternator and regulator for you to check out Paul. Thanks for the help!!

 

[LUBr LuvR]

Following this as I have a similar issue on a ‘74.

Paul, hope someday you get to come east and meet some of us who benefit from your vast knowledge. Then you’d see why I dang near spewed my coffee when read this, and your current audience.....;D;D;D

“Have any buddies with older Fords nearby?“

Hope you get Rattler sorted out soon!

 

[DirtDonk]

Thanks! Hope I get to travel out that way someday too. Been looking forward to it for a long time now.

Just thought of another thing along the same lines as the corrosion buildup. There's one more connection that needs to be inspected. If not regularly (it's pretty well sealed usually) then at least once every 40 years or so.;D
That's the plug/connector just near the back of the ammeter, along that Black w/yellow wire. It's the main wire disconnect and while most of them are in perfect shape, some (especially in moister climates, nudge nudge, wink wink...) can experience deterioration too.
So while you're at this connection-inspection (that should be a Bronco catch-phrase to help remember regular maintenance), you can pull that one apart too and inspect for either/or/both looseness, and corrosion buildup.

Even if it does not cause the oscillating, it's not good for the overall health of the Bronco's wiring system.

Paul

 

[DirtDonk]

Now remember too, all this discussion of wiring is due to the fact that you mentioned that you could see the lights flickering as well. If it was just the needle jumping, but not associated with any obvious electrical effect, the ammeters do lose their dampening ability over time sometimes.
Some of us are lucky and the gauge lasts the life of the vehicle, while others have gone bad less than ten years after the Bronco was built.

As soon as you see flicking in the electrics though, then you know it's not just the gauge, but something going on elsewhere.

Paul

 

[gr8scott]

Installing a headlight relay harness can do wonders too. It'll take the load off the headlight switch, should stop the flickering and make them brighter.

https://www.tomsbroncoparts.com/product/Heavy-Duty-Headlight-Wiring-Harness-66-77-ford-bronco-new

 

[blubuckaroo]

I was just wondering if a alternator diode could cause this oscillation?

 

[Broncobowsher]

Isn't there suppose to be a noise condenser for the field?

 

[blubuckaroo]

Isn't there suppose to be a noise condenser for the field?

Watching this...
I have a wig-wagging ammeter too.

 

[DirtDonk]

The noise capacitor/condenser/thingy was on the Yellow "A" battery sensing wire.
But it's not impossible for them to go bad too, partially shorting to ground through their case. Acts like a load more than a short, and does not even melt the wire.
But the one on the ignition coil can kill the spark output for disrupting the power. Reasonable to think it might have some strange effect on a charging system as well.

Paul

 

[bmc69]

Paul correctly noted that the ammeter is a passive sensing device. However, due to the nature of its construction, the dynamic response of the needle is second order, meaning it has a very distinct natural frequency. If the excitation amperage includes any ripple at that frequency, the needle can be driven unstable.

FWIW I use Newmar in-line noise filters in a lot of my rigs to eliminate alternator ac noise.

 

[gr8scott]

FWIW I use Newmar in-line noise filters in a lot of my rigs to eliminate alternator ac noise.

Something like this?

https://powerwerx.com/newmar-150a-alternator-line-noise-filter

 

[bmc69]

Something like this?

https://powerwerx.com/newmar-150a-alternator-line-noise-filter

Exactly like that.

 

[Bronco4x4]

Cool stuff. Impressed as always from this site.