Truck Died Instantly - Electrical Smoke/Smell

[rockyrivermark]

I would buy a new one wire internally regulated alternator.
They are reasonably priced

[harrydunn]

Originally Posted by rockyrivermark

I would buy a new one wire internally regulated alternator.
They are reasonably priced

Down the road perhaps but I don't want to add any more variables to figure out the issue at the moment.

[MARKDTN]

I would take the alternator and have it tested. I believe you have an internal short. This would be a great time to convert to an internal regulated alternator. I would NOT do a 1-wire version. It is a bolt-on swap with minimal wiring.

[harrydunn]

Originally Posted by body bolt

I second this although his alternator does appear to be internally regulated.

I’ve still got an external regulator with all wiring in place running to the ALT.
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[Stocker]

Input which I found helpful -- from Andy, in my old thread

Originally Posted by Andy4639

Just some food for though.
A 1 wire alternator will work but it want have the capability to control the charge like the 3 wire.
A 1 wire will charge at the same amount no matter what the load is on the battery are the rpm of the motor, where a 3 wire will only charge at a rate enough to keep the battery at a constant charge so it want ever under charge it are over charge it.

[harrydunn]

Bad alternator. One new fusible link soldered in and one new alterntor and she is purring like a kitten again. Am I correct that when the diodes fail in the alternator it allows current to flow from the battery to the alternator, thus causing the heat and smoke?

[54blackhornet]

For some very interesting information about wiring in a alternator google MAD Electrical...I one wire is not the preferred upgrade for most applications.

[Steeveedee]

Originally Posted by harrydunn

Bad alternator. One new fusible link soldered in and one new alterntor and she is purring like a kitten again. Am I correct that when the diodes fail in the alternator it allows current to flow from the battery to the alternator, thus causing the heat and smoke?

That's a very common failure mode. I've seen brand new vehicles with popped fusible links, fwiw. I've had TWO rebuilt alternators with failed diodes, but by small leakage, so the battery went dead over some time, as opposed to in a "short" time, like yours did, frying the fusible link. The first time it happened, I was charging the battery back up and, looking the system over, noticed that the alternator was hot. Yup, bad diode. Back to the parts store it went. The second one did the same thing! I have my old alternator, which only needed a drive end bearing. But I couldn't get the thing out of the frame, so I had to buy a rebuilt (no core). Someday, I'll get it apart.

[Stocker]

Glad you got it fixed!

[harrydunn]

Originally Posted by Stocker

Glad you got it fixed!

Appreciate your help, Mike!

-Mark

[harrydunn]

Few more pics. Soldering the thick wire to the much thinner fusible link, heat shrink and the new alternator.

[HO455]

Originally Posted by harrydunn

Bad alternator. One new fusible link soldered in and one new alterntor and she is purring like a kitten again. Am I correct that when the diodes fail in the alternator it allows current to flow from the battery to the alternator, thus causing the heat and smoke?

Nice work on the repair!

Unfortunately there isn't one definite symptom that occurs when a diode(s) fails. They can short across, they can open internally, or they can degrade and operate out specification or intermittently.
Diodes are simple and pretty tough so it is usually some other component in the circuit that fails and takes the diode out.

[harrydunn]

Yah, I actually enjoy electrical on my other vehicles--adding relays for lights, etc but I had not had to do any electrical at all on my '72 since owning it. Hey, quick question. This new alternator is clocked 90 degrees off. Can I just take out the perimeter long bolts and clock it how I want?

[HO455]

Yes you can. Quick video on how to.

https://www.youtube.com/watch?v=91lfKtbU7ew

[Steeveedee]

Originally Posted by HO455

Nice work on the repair!

Unfortunately there isn't one definite symptom that occurs when a diode(s) fails. They can short across, they can open internally, or they can degrade and operate out specification or intermittently.
Diodes are simple and pretty tough so it is usually some other component in the circuit that fails and takes the diode out.

In my experience, taking the hot cable off the battery with the engine running to see if the charging system is working (never did this!) pretty much assures a blown diode. I used to manage a shop, and I can't tell you many parts changers I had to educate to use the correct equipment that we had, right there in the shop. In my case, the truck worked just fine if it was driven all the time, so it wasn't until it sat for a couple of weeks that the battery was found stone bone dead. Bad diodes don't always cause what we've seen here.

[dmjlambert]

Originally Posted by Steeveedee

In my experience, taking the hot cable off the battery with the engine running to see if the charging system is working (never did this!) pretty much assures a blown diode.

Are you saying taking the hot cable off the battery with the engine running may cause a diode to blow?

[garyd1961]

Originally Posted by Steeveedee

In my experience, taking the hot cable off the battery with the engine running to see if the charging system is working (never did this!) pretty much assures a blown diode. I used to manage a shop, and I can't tell you many parts changers I had to educate to use the correct equipment that we had, right there in the shop. In my case, the truck worked just fine if it was driven all the time, so it wasn't until it sat for a couple of weeks that the battery was found stone bone dead. Bad diodes don't always cause what we've seen here.

I know there are vehicles that you cannot leave running while changing a battery, I'm pretty sure VW is one. I never liked leaving any vehicle running with the battery disconnected but when I went to work at a Toyota dealership I was told to always leave them running. I didn't listen at first but one day when I cranked a car after installing a new battery the car ran like crap. I found that when you disconnect the battery the computer resets to factory settings. The problem is you now have dirty injectors and a gunked up motor that the computer was compensating for. Now you have to run the car for 30 minutes or longer for the computer to reprogram itself while the customer is asking where is my car.
I never had a problem with one of these old trucks though. We would pull a cable of back in the day just to see if it was charging. Now I use a tester for that though.

[body bolt]

Why didn't your dealership put another 12V source on the electrical system instead of leaving the engine running to supply it? A very small 12V battery has enough capacity to hold ECU data for hours.

Originally Posted by garyd1961

I know there are vehicles that you cannot leave running while changing a battery, I'm pretty sure VW is one. I never liked leaving any vehicle running with the battery disconnected but when I went to work at a Toyota dealership I was told to always leave them running. I didn't listen at first but one day when I cranked a car after installing a new battery the car ran like crap. I found that when you disconnect the battery the computer resets to factory settings. The problem is you now have dirty injectors and a gunked up motor that the computer was compensating for. Now you have to run the car for 30 minutes or longer for the computer to reprogram itself while the customer is asking where is my car.
I never had a problem with one of these old trucks though. We would pull a cable of back in the day just to see if it was charging. Now I use a tester for that though.

[Steeveedee]

Originally Posted by dmjlambert

Are you saying taking the hot cable off the battery with the engine running may cause a diode to blow?

Yes.

[body bolt]

I agree. It's a big no-no.

Originally Posted by Steeveedee

Yes.

[Steeveedee]

Originally Posted by garyd1961

I know there are vehicles that you cannot leave running while changing a battery, I'm pretty sure VW is one. I never liked leaving any vehicle running with the battery disconnected but when I went to work at a Toyota dealership I was told to always leave them running. I didn't listen at first but one day when I cranked a car after installing a new battery the car ran like crap. I found that when you disconnect the battery the computer resets to factory settings. The problem is you now have dirty injectors and a gunked up motor that the computer was compensating for. Now you have to run the car for 30 minutes or longer for the computer to reprogram itself while the customer is asking where is my car.
I never had a problem with one of these old trucks though. We would pull a cable of back in the day just to see if it was charging. Now I use a tester for that though.

The right way to do that is use a 9V battery plugged into an accessory port to avoid having the ECU losing its tiny little mind, or more importantly, losing radio presets. The ECU will relearn driving conditions within a relatively short rime.

You're lucky you didn't pop a diode, BTW. As has been mentioned, they're pretty robust...