Alternator not turning on?

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1993 FZJ80, photoman sequoia alternator done in 2015 with take-off OEM alt from an '02.

Last week I got the christmas tree lights. I figured on a 20yo alt that was to be expected. Sure enough no charge coming from it.

I replaced it with a box-store alt with lifetime warranty. Fired the truck up and got 14v, looked great. I drove off and 5 miles later - christmas tree lights.

Pulled the alt and took it in under warranty and got another. Hooked it up and fired up the truck, 14v, great. 5 miles later christmas tree lights.

I took it in and they said the battery tested good and the alt wasnt turning on.

I dont believe I got 3 bad alts, including an OEM. I checked the charge fuse in the engine bay and it tested good. What else could it be? Is there a signal to "turn on" the alt?
 
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I dont believe I got 3 bad alts

I do. I wouldn't trust a parts store rebuild. It's easy to have a rebuild that looks good initially but has a bad regulator/rectifier.

That said, if I recall correctly you have to change the plug on the end of the harness to connect to the Sequoia/Tundra alternator. Have you inspected that to make sure the pins are properly seated and the wires are intact?

The first thing I would do, though, is verify the actual voltage at the battery when the "Christmas tree" condition happens, using a multimeter.

Also, do you have any LED bulbs in the gauge cluster? That can cause all kinds of fun stuff to happen.
 
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Yes on the LED's. I have had them for many years. I did switch the plug, I wouldn't expect that to suddenly go bad though.

While getting the dash lights I had ~9v at the battery, engine running or off, same thing.
 
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9V at the battery is a dead battery that might only be able to slow crank the starter... I can't imagine a battery that has 9V on it after a few minutes of running could have actually been able to start the engine in the first place.

I assume you're using a decent meter and probing right on the lead terminals of the battery?

cheers,
george.
 
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While getting the dash lights I had ~9v at the battery, engine running or off, same thing.

There's no way that's accurate.

A healthy, charged 12V battery at rest should be about 12.5 - 13V. Ignition on without the engine running should be about one volt lower. You should never see 9V on a 12V battery, except maybe momentarily while cranking the starter. Even then, on the LC, I don't think I've seen less than about 10.7V.
 
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There's no way that's accurate.

A healthy, charged 12V battery at rest should be about 12.5 - 13V. Ignition on without the engine running should be about one volt lower. You should never see 9V on a 12V battery, except maybe momentarily while cranking the starter. Even then, on the LC, I don't think I've seen less than about 10.7V.
I think at that point I had been running the engine on the battery alone, so it was severely depleted, its also possible I measured from a corroded location on the battery terminal and it wasn't a clean measurement.

Looking at the wiring diagram it looks like there is a 12v wire from the battery to the alt via the fusible link and then also a 12v switched line coming from the ignition circuit. The 3rd wire in the connector appears to be going to the charge indicator lamp. I'll probe the two charged wires to see if they are passing current as expected. If they are, it has to be the alternator. If not, I've got a different issue.
 
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I think at that point I had been running the engine on the battery alone, so it was severely depleted, its also possible I measured from a corroded location on the battery terminal and it wasn't a clean measurement.

Looking at the wiring diagram it looks like there is a 12v wire from the battery to the alt via the fusible link and then also a 12v switched line coming from the ignition circuit. The 3rd wire in the connector appears to be going to the charge indicator lamp. I'll probe the two charged wires to see if they are passing current as expected. If they are, it has to be the alternator. If not, I've got a different issue.
original fusible links? might be time to swap out to new ones as they can cause issues when on the way out
 

landtank

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Unwrap the fusible links and check the blue link specifically. That’s the link from the alternator to the battery for charging.

Most people are just installing these 150 amp alternators and not resizing that link appropriately as well as the charging wire.

So in your situation the first alternator died and you drained the battery down.

Then you replaced the alternator and started to drive the truck and the alternator kicked in and started charging the battery.

The issue is it is passing 150 amps through a link sized for only 80 amps.

If you replace that link with another stock link you should fully charge the battery off line before driving the truck.
 
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Unwrap the fusible links and check the blue link specifically. That’s the link from the alternator to the battery for charging.

Most people are just installing these 150 amp alternators and not resizing that link appropriately as well as the charging wire.

So in your situation the first alternator died and you drained the battery down.

Then you replaced the alternator and started to drive the truck and the alternator kicked in and started charging the battery.

The issue is it is passing 150 amps through a link sized for only 80 amps.

If you replace that link with another stock link you should fully charge the battery off line before driving the truck.
I did upgrade my b+ line many years ago and installed a Blue Sea 200A fuse. The fusible links (Main & AM1) are factory links with a couple of years on them.

I also should have mentioned I upgraded all my charging and ground wires a few years ago and switched to marine/military battery terminals.

I'll also test my fusible link (AM1 - blue wire) this evening. Good suggestion.

20221012_073210.jpg
 

landtank

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if you ran a separate wire to a 200 amp fuse to the + battery terminal you should have removed the blue fusible link completely as well as the original +B wire from the alt terminal to the Battery terminal. You have two different wire gauges running in parallel carrying the Amps proportioned to their size while both being fused.

I chose to run a sister wire to share the load equally and then a single fusible link to protect the alternator.

You might want to clean that up some. And the fusible link is there to guard against an alternator short which would cause amps to flow to ground through that short and having a potential fire hazard. You want that fuse as small as possible but still be able to provide the rated Amperage without harming the link.
 
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Im at a bit of a loss, and need help from folks smarter than me.

When I first fired it up today, it ran for a good 10mins just fine, I was getting 14v at the battery. I turned the truck off and then restarted it, and from then on the alt wasnt providing any charge. Multiple restarts after that and the dash lights showed it would work for a few seconds after first starting (maybe a self-check period?) and then not work.

Fusible links tested good. I removed the alt A connector and tested per the FSM. I got the expected 12v (battery voltage) from the A1 wire, and on the A2 wire where I was supposed to see 0-4v with the ignition ON but not running, I got battery voltage (plug disconnected from the alternator.) That wire runs through the 7.5A fuse in the engine bay marked "charge". When its plugged into the alt I get .08v on that line. The FSM doesn't specify if I should test it plugged or unplugged.

I unwrapped my wires back to the splices and they still look good, soldered and heat-shrinked and good continuity across them.

I guess my question is: with everything hooked up, should I be getting 0-4v on the 7.5A Charge fuse in the engine bay with the key switched ON and engine not running? And if I unplug the alt A plug, should that fuse jump to battery voltage? I cant tell if that's normal behavior and therefore my alt is bad, or if that's incorrect behavior and the problem is something else in the truck and its killed the IC regulator in 3 alternators.
 
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if you ran a separate wire to a 200 amp fuse to the + battery terminal you should have removed the blue fusible link completely as well as the original +B wire from the alt terminal to the Battery terminal. You have two different wire gauges running in parallel carrying the Amps proportioned to their size while both being fused.

I chose to run a sister wire to share the load equally and then a single fusible link to protect the alternator.

You might want to clean that up some. And the fusible link is there to guard against an alternator short which would cause amps to flow to ground through that short and having a potential fire hazard. You want that fuse as small as possible but still be able to provide the rated Amperage without harming the link.

Ok, help me out with this as I want the cleanest/safest setup possible:

Currently I have a 0awg wire from B+ on the alt through a 175A fuse (sorry, I was going from memory early when I stated 200A) to the + end of the battery. Separately I have another 0awg wire going to the starter and 3 fusible links going into the harness: the 2 in the black box (Main & AM1) and then a 3rd separate pink wire that goes into its own connecter and then into the harness. Those are all OEM. Honestly its been like 7yrs since I did the alt conversion, I thought I remember looking at the fusible links and thinking they went to some things I still needed, so I left them. Happy to be corrected on that though.
 

landtank

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I don’t see the need to alter the starter wire because of the upgrade.

If you look at the MAIN connection there is a white 8ga wire that connects to the alt+ connection and a blue wire (fusible link) that connects to the battery terminal.

This is the factory line for charging the battery.

You added a 0ga wire with a 175amp fuse that connects to the alt+ connection to the battery.

These two lines are in parallel to each other and influence how the power is transferred to the battery.

You really only want a single path and a single fuse.

At minimum I’d remove the blue fusible link that goes from the MAIN connection to the battery. The white wire would just dead end on the MAIN stud.
 
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Can I get someone to do me a small favor?

I dont have a baseline to test against, can someone go out to their 80 and with the key in the "On" position (engine not running) measure the voltage in the 7.5A CHARGE fuse in the engine bay? And then repeat with the A connector removed from the alt?

Alt plugged in:

20221014_161036.jpg


Alt unplugged:

20221014_161050.jpg


Need to confirm if a known good system behaves the same.
 
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I did a little more testing and the charge fuse should have battery voltage once the engine starts and runs.

Well dangit, Im definitely not getting that. With the engine running Im only getting .08v on that 7.5A fuse. Unless I unplug my alt, then it jumps to batt voltage. Thanks for taking that extra step.

FYI - off the truck my alt tested good. It was only at one box store and I know thats not totally reliable, so I am going to take it to another couple of places to get tested. But Im back to my original hypothesis of it not being the alternator at all.
 

landtank

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Well dangit, Im definitely not getting that. With the engine running Im only getting .08v on that 7.5A fuse. Unless I unplug my alt, then it jumps to batt voltage. Thanks for taking that extra step.

FYI - off the truck my alt tested good. It was only at one box store and I know thats not totally reliable, so I am going to take it to another couple of places to get tested. But Im back to my original hypothesis of it not being the alternator at all.
Typically a loss of voltage is do to a bad connection. That bad connection can’t pass the needed amperage to main rain the voltage.

Pull the fuse and check it again. If the voltage is constant I’d suspect the plug and residing you did going from a 3pin to 4 pin connector.
 

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