1973 FJ40 New Alternator Not Charging

[ASO544]

So ….. started some work on my FJ40 and I replaced the alternator with a new one as the old one was looking…. Well…. Really old and not charging .

Got it replaced and was charging fine ( 13.7-14.0 Amps ) for a few weeks then I noticed yesterday it wasn’t charging. I could tell as my 30 amp gauge was stuck dead center or slightly lower and my Sniper digital display has it at 11.9-12.0 with a yellow light where is was usually 13.7-14.0)

I checked all the connections at the battery , alternator, and the Voltage Regulator and all were good and clean. I also replaced the External Voltage Regulator as I had an extra new one…. Still no charging when idle or driving at speed.

Guess im kinda lost at this point. Im sure its possible the Alternator went bad with todays workmanship but any other test I can do at home before I try and drive it to the local parts store to test the alternator.

 

[ASO544]

 

[Mark Jennings]

Double check your engine/chassis ground. If needed, you can get one these from Harbor Freight. For the alternator check, it’s basically a voltage meter but it has a ‘toaster wire’ to load the system. That’s basically all Autozone or O’Rileys does/uses.

Also, where did you get the alternator? Just curious. The stock FJ40 ran a 45 amp alternator. With AC and/or FI, should run a minimum 50 amp, 60 amp would be even better….or a GM 100 amp.

I think the older Corolla alternators, that are direct bolt on for our 40’s is 50 amp.

 

[ASO544]

I actually got one of those but wasn’t 100% sure how to use it to test an alternator but looked it up.
It has 12.4 volts at the battery a hair lower under load. It was in the low range while running in the charging system

The chassis /engine ground looks great

I got the alternator from city racer…. 50amp

Guess I could take my old one and put it back in… if it charges the system then I know it’s the new alternator .

 

[B y r o n]

. . . The chassis /engine ground looks great . . .

Did you simply do a visual inspection or did you remove the bolt and wire brush everything before putting back together? Oxidation can form on the bolt threads, chassis and the eyelet on the ground cable. Once that happens you don't have a ground that is 100%. It may look good from the outside but not making 100% contact like it should.

 

[Mark Jennings]

Another thing you could do is run a temp ground from the alternator back to the negative side of the battery. Retest and see where it runs. Also, put a load on the battery, e.g. turn on the headlights, run the wipers, turn on the 4 ways…..
Maybe even discharge the battery a bit before you start the rig to retest. The voltage regulator only allows the alternator to charge once the voltage is below a certain threshold. I notice that on my rig, it’s only 14.5 volts for a short period to charge the battery, then drops to 13 volts once the battery is charged.

 

[swixtt]

I’d drop the old back in and see what you get. Mine did this too.

 

[ASO544]

Regarding the temp ground….which connection on the alternator do I run it from to the neg on the battery ?

I’ll bleed the battery down some and try this test……If it doesn’t work I’ll pop the old alt back on.

Another thing you could do is run a temp ground from the alternator back to the negative side of the battery. Retest and see where it runs. Also, put a load on the battery, e.g. turn on the headlights, run the wipers, turn on the 4 ways…..
Maybe even discharge the battery a bit before you start the rig to retest. The voltage regulator only allows the alternator to charge once the voltage is below a certain threshold. I notice that on my rig, it’s only 14.5 volts for a short period to charge the battery, then drops to 13 volts once the battery is charged.

 

[Mark Jennings]

Regarding the temp ground….which connection on the alternator do I run it from to the neg on the battery ?

I’ll bleed the battery down some and try this test……If it doesn’t work I’ll pop the old alt back on.

Just clip it to one of the mounting bolts or anyplace on the alternator housing. You’re just looking to see if the circuit is complete between the alternator body back to the negative side of the battery.

 

[charliemeyer007]

+1 for looks clean is always correct! Corrosion can crawl under the insulation at the connector and rot the wire while passing the it looks clean test. Use your VOM and check the wire's resistance, continuity isn't always enough. Fold a piece of crocus cloth in half and pull it threw the regulator points once or twice to polish them.

Even the best rebuilt or new parts can fail.

Putting the old stuff on is such an easy test.

 

[ASO544]

The ground is clean and well grounded.no issues there. I did put the old one back on but it isn’t charging either. To be honest I now remember it was really charging or charging that well when it came off.

I guess I can take the new one to the local store to bench test it. Kinda weird cause it was charging fine on my ride home. The only electrical thing I’ve done between this is swap a radio but it was super simple although I didn’t unhook the battery. Of course I’ve swapped radios a few times and never unhooked the battery before .

Ive checked all fuses and connections and there is 12v at the B connector on the alternator

 

[ASO544]

Ok….. I took the alternator for bench testing and it passed 3 test.

I have another VR I can try as well but I’m guessing it’s in the wiring possibly

 

[ToyotaMatt]

So ….. started some work on my FJ40 and I replaced the alternator with a new one as the old one was looking…. Well…. Really old and not charging .

Got it replaced and was charging fine ( 13.7-14.0 Amps ) for a few weeks then I noticed yesterday it wasn’t charging. I could tell as my 30 amp gauge was stuck dead center or slightly lower and my Sniper digital display has it at 11.9-12.0 with a yellow light where is was usually 13.7-14.0)

I checked all the connections at the battery , alternator, and the Voltage Regulator and all were good and clean. I also replaced the External Voltage Regulator as I had an extra new one…. Still no charging when idle or driving at speed.

Guess im kinda lost at this point. Im sure its possible the Alternator went bad with todays workmanship but any other test I can do at home before I try and drive it to the local parts store to test the alternator.


View attachment 3611285View attachment 3611287View attachment 3611289View attachment 3611290View attachment 3611291

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the original Genuine NipponDenso japan spec. unit installed at the factory in japan , most likely lasted 10-15+ years or more


that unit is remanufactured in China , and or deep south mexico ....


the voltage regulator in your photo above , is the same topics , new maybe yes , but

the original 27700- made in japan DENSO , is a rock solid piece of iconic land cruiser parts


i always no matter what , replace the regulator with ANY new alternator , never exception


when you buy new shoes , you install shoe laces , ,,,,that is all you need to relate it with , not doing so , your cheating fate in low odds in your favor way ...



enough said there ........


you have a drivers side lower mounting location LHD land Cruiser , this is a good thing here ,

,


this is a 100% new , not reman Genuine NipponDenso japan Spec, 45A example of a p[lug and play correctly clocked mounting tabs etc


the voltage regulators below can have a locking latching modern connector plug or the early 3 screw termianls if you like living on the wild side on the attachment points method topic

.

below are higher AMPS 50A , 55A 60A and 65A


your truck came with the 45A or a optional cold spec. SNOW VERSION 50A ,.....

not higher then that , your white wire and white wire w/ blue tracer stripe would need to be upadated to the correct 10ga to go higher ....fyi this is a topic NOT to dismiss ...


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[jbee]

I got a DOA one from o’reilly last year and got a bad one from rockauto before.
It’s rare but it happens.

 

[ASO544]

Doing some looking and trying to figure out how the charge from the alternator gets to the battery.

1. The big red one goes to the starter
2. The white one with the plug must come from the fuse box as it powers my Sniper / display module when touching the post.
3. The plain red one powers the electric fuel pump
4. The red with blue connectors…. No idea what it does but it doesn’t have power coming to it unhooked from the battery so it’s not bring charge from the alternator.

How does the alternator usually get the charge back to the battery…

 

[ToyotaMatt]

Doing some looking and trying to figure out how the charge from the alternator gets to the battery.

1. The big red one goes to the starter
2. The white one with the plug must come from the fuse box as it powers my Sniper / display module when touching the post.
3. The plain red one powers the electric fuel pump
4. The red with blue connectors…. No idea what it does but it doesn’t have power coming to it unhooked from the battery so it’s not bring charge from the alternator.

How does the alternator usually get the charge back to the battery…

View attachment 3612242

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please keep in mind your good solid tech questions above , are best explained using all the styles / type of General Circa. Era Vintage Toyota 12V Charging system technology details and examples below .....



you have a F.E.N. system

F = Field

E = Earth

- N = Neutral

.

.

Below FEN comprehensive TECH diagram courtesy of :

@ bj40green ​

.​

 

[ASO544]

I’m going to check today to see if power is getting to my VR from the Engine fuse. With the key in or the vehicle running. If I unplug the VR…. There should be 12v on one of the wires ( IG) correct ??

If so….What color is that wire ?

 

[Mark Jennings]

Thread 'Voltage Regulator (ext.) / How it works'
Voltage Regulator (ext.) / How it works - https://forum.ih8mud.com/threads/voltage-regulator-ext-how-it-works.747718/

I think you should read this before you continue. Old Ih8mud post on voltage regulator function….i think it will help you troubleshoot your issue.

 

[ASO544]

Whew…. That was a lot !!!!

Ok… so I checked my Engine Fuse ( 2nd from bottom) and the wire on the rear of the fuse box from that spot and I have 12v with the key on at the fuse and the wire in the rear.

This is the color wire that leaves the fuse box from the “Engine” fuse and goes into the harness that goes into the engine bay.

The harness then of course breaks out these 3 wires ( RW, GW, BW ) that plug into the VR.

Here is the plug but at no point with the ignition on or with the engine running do I get any power on any of these plug slots with my test light.

So am I right to think that I possibly have a short or break in the wire from the Engine fuse that should be carrying the 12v to the ING wire ( RED / WHITE) for the VR plug ?

 

[Coolerman]

The regulator fuse on a 1973 FJ40 is fuse 6 (Hazard fuse) not fuse 7 (Ignition) . It should be a Green/Red wire at the fuse panel. Inside the harness the White/Red wire is spliced to the Green/Red wire and goes out to the regulator three pin connector. See diagram