Diagnosing a charging issue (1 Viewer)

[DCAlbarran]

Hello all. Trying to diagnose a charging issue with our 64 FJ45. F engine, original (looking) alternator, newer looking voltage regulator. Newer (within the last year) interstate battery.

Haven’t had a problem with the truck until one day I went out to take my older son to karate and it cranked like it had a dead battery. Weaker and weaker until it wouldn’t crank at all. We had been out at night the day before and had the lights and heater fan going. Jumped into the minivan as we were already running late. Came home and put it on the charger, and started right up the next morning, and drove around town for an hour or two.

Now, just sitting there, the battery reads 12.35-12.4 volts. Started up and running, reads 12.2-12.3 volts with no accessories on. With lights and heater on, it reads 12.05-12.1 volts. When I turn the accessories off, it eventually climbs back up to 12.3 volts where it stays.

Higher RPMs do nothing to change the voltage.

Alternator tests good at pep boys, and I get a reading of 12.3 at the alternator. I had swapped in a rebuilt unit before I got the old one tested, but there was no voltage change, so I guessing it’s not the alternator.

Swapped the voltage regulator for a new one, no change.

Thoughts from the brain trust?

 

[snaggletto]

I’m thinking you should be seeing more like 12.8-13 vdc at the battery while charging with minimal load. There are some good write ups here on voltage regulators you should read up. Maybe check old wiring for voltage drop as well.

 

[Solace in Solitude]

Rudi explains how a voltage regulator works, in this link, and how to adjust the regulator to properly charge... you need to be turning >= 2000rpms to actually make the alternator charge.

Read this and thank @bj40green —>Voltage Regulator (ext.) / How it works

 

[Coolerman]

Check to see if your Amp Meter is working. If it has failed you will get no charge going to the battery. You can bypass it if it has by just putting both the White and
White/Blue wires on one post of the Amp Meter.

Also check the fuses...

 

[DCAlbarran]

Thanks for the replies. How can I check if the amp meter is working?

 

[73FJ40]

Thanks for the replies. How can I check if the amp meter is working?

Does the needle move? With engine off, turn on headlights. Ammeter should go down scale.

With engine running, rev the engine to 2000 rpm or more (don't over do it) and see if the needle moves. Needle should move upscale.

 

[DCAlbarran]

There’s no ammeter, just an idiot light.

 

[73FJ40]

There’s no ammeter, just an idiot light.

Maybe revisit your first post regarding what's original or not in your truck. Pictures would help immensely.

 

[DCAlbarran]

Maybe revisit your first post regarding what's original or not in your truck. Pictures would help immensely.

It’s stock mostly under the hood. They didn’t come with ammeters in 1964.

 

[DCAlbarran]

Pics

 

[DCAlbarran]

Again, it IS charging. Despite everything, always comes back to 12.35-12.4 volts eventually. Just not enough to keep up with demand sometimes if I have multiple accessories running.

 

[middlecalf]

It’s stock mostly under the hood.

Not really at all electrically.

 

[DCAlbarran]

Not really at all electrically.

Aside from some newer than 1964 wiring, the charging side is stock, at least to my admittedly limited knowledge. If there is something you see that I am missing that could be causing my charging issue, please don’t hold back. I am stumped.

 

[Cromagnon]

As long as the system IS charging what is the problem you are experiencing? Are you using a wet lead acid battery? Do you believe that 12.4VDC is a full charge state for your battery? You should see a + ammeter needle deflection or no idiot light and a voltage greater than 12.4VDC with the engine rpm at or greater than 2000. If this is not true then your system is not charging. Troubleshoot your charge circuit looking for bad fuses / fuseable links, poor crimp connections, corrosion, shorted / burned wiring, broken wires and missing connections. Use the wiring diagrams and double check all of the charging circuit for propper connectivity.

 

[DCAlbarran]

As long as the system IS charging what is the problem you are experiencing? Are you using a wet lead acid battery? Do you believe that 12.4VDC is a full charge state for your battery? You should see a + ammeter needle deflection or no idiot light and a voltage greater than 12.4VDC with the engine rpm at or greater than 2000. If this is not true then your system is not charging. Troubleshoot your charge circuit looking for bad fuses / fuseable links, poor crimp connections, corrosion, shorted / burned wiring, broken wires and missing connections. Use the wiring diagrams and double check all of the charging circuit for propper connectivity.

I didn’t know that I was having a problem until it wouldn’t start one evening. It has has not problem starting, running, using all accessories, etc. since I’ve had it. Not starting is what caused me to check the voltage etc. and that’s when I found that I’m maxing out at 12.4 volts.

Working from there, I checked alternator and voltage regulator and those both checked out fine. When I check the charge at the alternator itself I’m getting the same 12.4 as the battery, so I am wondering why the alternator isn’t giving more voltage.

 

[Cromagnon]

I wo

I didn’t know that I was having a problem until it wouldn’t start one evening. It has has not problem starting, running, using all accessories, etc. since I’ve had it. Not starting is what caused me to check the voltage etc. and that’s when I found that I’m maxing out at 12.4 volts.

Working from there, I checked alternator and voltage regulator and those both checked out fine. When I check the charge at the alternator itself I’m getting the same 12.4 as the battery, so I am wondering why the alternator isn’t giving more voltage.

I would say the system is not charging. You have tested the alternator and it tested good. You swaped out the voltage regulator for an assumed known good one. The only other active component is the battery. If it had a shorted cell it would likely be below 12.4VDC, so I think we can call that good. Next up is the wiring. Get a good diagram of the charging system and multimeter and start from one end to the other. Make sure you disconnect the battery before taking any continuity measurements. The last thing is to let us know what you find regardless how insignificant you think it may be. The little things are the hardest to find. Good luck!

 

[middlecalf]

On your voltage regulator where does the wire that’s connected to the IG terminal go? Also, what happens to the wire from the N terminal on your alternator - I can’t tell from your pics - I only see 3 wires downstream from the 4 that are connected to it.

 

[fjc-man]

If it was charging, you would see running voltage somewhere between 13.5 and 14.8V

 

[DCAlbarran]

On your voltage regulator where does the wire that’s connected to the IG terminal go? Also, what happens to the wire from the N terminal on your alternator - I can’t tell from your pics - I only see 3 wires downstream from the 4 that are connected to it.

 

[middlecalf]

Ok so the N terminal wire goes no where, which is ok because that VR doesn’t have a connection for it (need a 6-wire VR) so that is why the AMP light doesn’t work (I’m assuming it doesn’t light when you turn the key to the first click which it should). The IG terminal wire on the VR (looks like a solid gray wire) is where the VR senses the voltage on the “system” and tells the alternator via the white/green wire (red wire off the F terminal on the VR) what to put out voltage wise. Where does it go?