Alternator Charging Issue

ledzilla · Nov 7, 2024

So, yes, looks like I have yet another alternator issue. I've had a few issues where I'd come out to my Bronco, but there wasn't enough juice in the battery for it to start. I ended up swapping batteries a couple times in the last month or so from the local junkyard (one battery wouldn't hold a charge at all). I was thinking that I had some sort of weird parasitic draw even though the only pull on the battery when not running was the radio's memory circuit (verified to be 0.3A draw when the battery connects and then reduces to below what my meter could read after several seconds, so less than 0.01A). So that wasn't the case. Then I noticed the last two times this occurred, I had driven some distance from home. I headed out in segmented runs, making stops and getting further. But it was just one straight shot home each time. No issues encountered while out and about, only after getting home and trying to start the Bronco again later on. The return journeys were all more than 30 minutes of driving with highway driving or travel on roads near highway speeds. On one of these drives, getting near home, I noticed the instrument cluster looked relatively dim and I tried fiddling with the dimmer switch, but it didn't help. Makes me think it was all running on reduced alternator output.

So, I'm of the mind that the alternator is the problem, but as with most things I don't think it has more than a one year length on the warranty. But assuming that it's not a quality issue with the alternator itself, could there be something else going on under the hood that could cause such an issue on longer drives like this? Maybe too much heat, something pulling an unexpectedly high draw on the alternator? Just want some things to look at before I try looking into replacing the alternator. I don't want to replace it only to have the same issue come back again.

L\Bronco · Nov 7, 2024

ledzilla said:
So, yes, looks like I have yet another alternator issue. I've had a few issues where I'd come out to my Bronco, but there wasn't enough juice in the battery for it to start. I ended up swapping batteries a couple times in the last month or so from the local junkyard (one battery wouldn't hold a charge at all). I was thinking that I had some sort of weird parasitic draw even though the only pull on the battery when not running was the radio's memory circuit (verified to be 0.3A draw when the battery connects and then reduces to below what my meter could read after several seconds, so less than 0.01A). So that wasn't the case. Then I noticed the last two times this occurred, I had driven some distance from home. I headed out in segmented runs, making stops and getting further. But it was just one straight shot home each time. No issues encountered while out and about, only after getting home and trying to start the Bronco again later on. The return journeys were all more than 30 minutes of driving with highway driving or travel on roads near highway speeds. On one of these drives, getting near home, I noticed the instrument cluster looked relatively dim and I tried fiddling with the dimmer switch, but it didn't help. Makes me think it was all running on reduced alternator output.

So, I'm of the mind that the alternator is the problem, but as with most things I don't think it has more than a one year length on the warranty. But assuming that it's not a quality issue with the alternator itself, could there be something else going on under the hood that could cause such an issue on longer drives like this? Maybe too much heat, something pulling an unexpectedly high draw on the alternator? Just want some things to look at before I try looking into replacing the alternator. I don't want to replace it only to have the same issue come back again.

Hey Led
do you know the battery voltage engine running?
It should be between 13.4 and 15.2 (depending on temp)
I'd measure DCV across the battery at 2000rpm.Then make the same measurement between the alternator B terminal and the housing. (also at 2000 rpm)
They should be pretty close to 2VDC higher than the battery, (engine off), and within .5V of each other.
If there is no charge, (Batt voltage doesn't rise), touch the rear bearing area of the alt (at idle) with a prybar or other metal tool and see if its magnetic.
No magnet means a brush or voltage regulator issue (Or primary power supply)
Magnet and no charge is a stator winding, diode, or output harness issue.

If it is charging, turn the headlights on, run at 2000rpm and measure A/C voltage between the alt B terminal and the housing. (This will test your diodes and stator windings)
It should be below .5V a/c at 2000rpm medium load (headlights)
Sorry for the blast of info.
Hope it helps.
Cheers

Tiha · Nov 7, 2024

Yep, check for over 13 volts when running, voltage should increase and not decrease if you rev the engine.

That era had a bad wire harness, for the longest time new alternators were coming with new harnesses so check that for burnt wires as well.

ledzilla · Nov 7, 2024

Well, I've already tested it to kick out approximately 14.5V at either fast or regular idle and only 0.10-0.15 volt drop with the lights on, and not running the voltage tested at something like 12.67V when I knew the battery was properly charged. The wiring is good. I upgraded the battery cable from the alternator to something like a 4ga battery cable last year. And that's the thing, that the charging is just fine when it isn't running for very long. I can go to the store, grab some food, or whatever when it seems like the engine won't be running for more than maybe 20 minutes.

I'm thinking maybe I should take one of these USB power ports I have sitting around and hook it up. They have a voltage display in the middle. Get it wired up and sit it on top of the dash, keep an eye on that actual voltage, see if I can identify when it drops or something.

L\Bronco said:
Hey Led
do you know the battery voltage engine running?
It should be between 13.4 and 15.2 (depending on temp)
I'd measure DCV across the battery at 2000rpm.Then make the same measurement between the alternator B terminal and the housing. (also at 2000 rpm)
They should be pretty close to 2VDC higher than the battery, (engine off), and within .5V of each other.
If there is no charge, (Batt voltage doesn't rise), touch the rear bearing area of the alt (at idle) with a prybar or other metal tool and see if its magnetic.
No magnet means a brush or voltage regulator issue (Or primary power supply)
Magnet and no charge is a stator winding, diode, or output harness issue.

If it is charging, turn the headlights on, run at 2000rpm and measure A/C voltage between the alt B terminal and the housing. (This will test your diodes and stator windings)
It should be below .5V a/c at 2000rpm medium load (headlights)
Sorry for the blast of info.
Hope it helps.
Cheers

So, the back of the alternator looks like the attached photo. Would the "B" terminal be the big red terminal?

L\Bronco · Nov 8, 2024

ledzilla said:
Well, I've already tested it to kick out approximately 14.5V at either fast or regular idle and only 0.10-0.15 volt drop with the lights on, and not running the voltage tested at something like 12.67V when I knew the battery was properly charged. The wiring is good. I upgraded the battery cable from the alternator to something like a 4ga battery cable last year. And that's the thing, that the charging is just fine when it isn't running for very long. I can go to the store, grab some food, or whatever when it seems like the engine won't be running for more than maybe 20 minutes.

I'm thinking maybe I should take one of these USB power ports I have sitting around and hook it up. They have a voltage display in the middle. Get it wired up and sit it on top of the dash, keep an eye on that actual voltage, see if I can identify when it drops or something.

So, the back of the alternator looks like the attached photo. Would the "B" terminal be the big red terminal?

You bet!
Let me know what you find.
Cheers

ledzilla · Nov 8, 2024

OK, so it's actually quite difficult to reach that terminal with the alternator installed, and I started getting a little panicky trying to reach it with the engine running, thinking I was going to mash my hand against the headers. So instead I touched the multimeter probe to the other end of the cable where it connects to a 350A bus bar (as seen on TV-- I mean in the attached photo). It gave me a reading of ~14V. I then tested against the battery terminals and got the same voltage reading.

L\Bronco · Nov 9, 2024

Ok cool, its charging and the cables look ok.
Do the A/C voltange check. Go from your bus bar and the alt housing (in A/C voltage mode) with the headlights on. Bring the rpm up a bit too.
You should see well under .5V a/c
A diode or stator winding could be bad, in which case it will appear to charge normally. The symptom you get sounds a lot like your issue.
Lets knock that one off the list, then move on
Cheers

ledzilla · Nov 9, 2024

Well, I took it for it's first drive around since repairing the exhaust the other day. I actually noticed several times that everything dimmed here and there. These instances weren't long, no more than a few seconds each time, but it's telling. I'm willing to bet that had I connected a multimeter or a voltmeter and watched the readouts each time the lights dimmed, there would have been a voltage drop from charge voltage to battery voltage.

Guess it's time to see whether or not the warranty has expired on that alternator.

ledzilla · Nov 11, 2024

So, yeah, the warranty expired a few months ago. I'm tempted to order a voltage regulator from somewhere like RockAuto and swap it out, just to rule out the alternator itself completely failing, since regulators are much cheaper than entire alternators, but I don't trust the quality of aftermarket regulators. I've had a lot of trouble with them on my '78 LTD.

ledzilla · Wednesday at 2:44 PM

I actually contacted Tuff Stuff to see if they have recommendations on replacement voltage regulators, given that for some reason they don't retail any replacements. No response at all. So, I'm not much inspired to give them any continued business should I need to replace the alternator. From what I can see, PA Performance offers replacement regulators, and I might just order one of theirs. They appear to be the same format that I need. Or maybe I'll grab one from RockAuto or Bronco Graveyard. Either way, the options all look pretty cheap to purchase.

johnnyreb · Wednesday at 7:49 PM

ledzilla said:
So, yes, looks like I have yet another alternator issue. I've had a few issues where I'd come out to my Bronco, but there wasn't enough juice in the battery for it to start. I ended up swapping batteries a couple times in the last month or so from the local junkyard (one battery wouldn't hold a charge at all). I was thinking that I had some sort of weird parasitic draw even though the only pull on the battery when not running was the radio's memory circuit (verified to be 0.3A draw when the battery connects and then reduces to below what my meter could read after several seconds, so less than 0.01A). So that wasn't the case. Then I noticed the last two times this occurred, I had driven some distance from home. I headed out in segmented runs, making stops and getting further. But it was just one straight shot home each time. No issues encountered while out and about, only after getting home and trying to start the Bronco again later on. The return journeys were all more than 30 minutes of driving with highway driving or travel on roads near highway speeds. On one of these drives, getting near home, I noticed the instrument cluster looked relatively dim and I tried fiddling with the dimmer switch, but it didn't help. Makes me think it was all running on reduced alternator output.

So, I'm of the mind that the alternator is the problem, but as with most things I don't think it has more than a one year length on the warranty. But assuming that it's not a quality issue with the alternator itself, could there be something else going on under the hood that could cause such an issue on longer drives like this? Maybe too much heat, something pulling an unexpectedly high draw on the alternator? Just want some things to look at before I try looking into replacing the alternator. I don't want to replace it only to have the same issue come back again.

When you get out. Have you c heck the brake lights? Sometimes the pedal will stick and the brake lights will run the batter down. Has anyone been having trouble NOT getting message from Bronco Zone ? I have --seems like they quit sending them to me. I hope they will start sending them to me again. Maybe its why we don,t see as many people on hear like we used to.

goodO1boydws · Thursday at 7:56 AM

This sounds like something that happened to me a long time ago. Have you double checked to see how good your ground cable connection from the battery is? If there's a weak connection on that one, say from rust/oxidation and/or a loose bolt, and its close to a heat source, the contact area may be opening up from heat expansion and breaking contact completely or be intermittent ONLY when it heats up enough. (Like during a long drive.) If that happens, the alternator wouldn't charge the battery-while that contact is open, and you'd be running on only the battery's voltage, like during a long drive. (which could explain the dim instrument lights. If that's what's going on, you might get the same results by letting the Bronc run for a good long while on your driveway. Or using a hair dryer, concentrating on the connection areas.

ledzilla · 2024-11-24T00:13:50-0700

johnnyreb said:
When you get out. Have you c heck the brake lights? Sometimes the pedal will stick and the brake lights will run the batter down.

Yeah, I always end up walking around behind it. The lights are always off.

ledzilla · 2024-11-24T00:19:06-0700

goodO1boydws said:
This sounds like something that happened to me a long time ago. Have you double checked to see how good your ground cable connection from the battery is? If there's a weak connection on that one, say from rust/oxidation and/or a loose bolt, and its close to a heat source, the contact area may be opening up from heat expansion and breaking contact completely or be intermittent ONLY when it heats up enough. (Like during a long drive.) If that happens, the alternator wouldn't charge the battery-while that contact is open, and you'd be running on only the battery's voltage, like during a long drive. (which could explain the dim instrument lights. If that's what's going on, you might get the same results by letting the Bronc run for a good long while on your driveway. Or using a hair dryer, concentrating on the connection areas.

I'm fairly certain the ground is good. It's a new terminal and cable, and I cleaned off the mount point on the block during installation. However, the last time I fired it up at night I noticed the dimming occurring immediately for a couple seconds each time. Things didn't have a chance to fully heat up and expand. But, I figure it can't hurt to double check the connection. With any luck I can do it myself, but I'm not sure with my hand all bound up right now. Might be too difficult to hold myself in place over the fender with a mangled thumb, but it's worth a try.

Alternator Charging Issue

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