Fluctuating AMP guage

[Finally Mine]

78 FJ40, Just back from vacation last week and noticed during driving that the amp guage fluctuates a significant amount between pos and neg. Any causes for this fluctuation? On start up guage is usually dead center, then after a few minutes starts dropping in the negative, with nothing other than the engine running. Thanks, Steve

 

[AdamKFarmer]

Voltage regulator?

 

[RadarFJ40]

Mine was doing the same. Got a Toyota replacement from Cruiser Corp. Problem solved.

 

[DSRTRDR]

the ammeter is telling you that you have a short or bad ground

 

[Pin_Head]

I vote for bad voltage regulator, bad alternator brushes or bad wiring between the two.

 

[bj40green]

I vote for bad voltage regulator, bad alternator brushes or bad wiring between the two.

I go with Pin_Head.

Rudi

 

[sggoat]

Claudia/Pin_head and FJ40Green--Listen to them
After startup, the ammeter should show a large charge, then reduce after a few minutes.-Sounds like the VR is acting up.

 

[Finally Mine]

I go with Pin_Head.

Rudi

Rudi, hello from Norfolk VA, how are things on the other side of the world? Changed out the voltage regulator only to notice no change in the AMP gauge. Something else I've noticed is some days it fires up like it was brand new, while other times it seems like its drained the battery. Will check the wires next for breaks etc, and if none, alternator? Steve

 

[bj40green]

Hi Steve,

We're in the green season (= commercial name for rainy season) right now. Which means; Hot and sunny in the morning and wet and humid in the afternoons afternoon.

On start up guage is usually dead center, then after a few minutes starts dropping in the negative, with nothing other than the engine running.

Changed out the voltage regulator only to notice no change in the AMP gauge. Something else I've noticed is some days it fires up like it was brand new, while other times it seems like its drained the battery. Will check the wires next for breaks etc, and if none, alternator? Steve

Sounds like; sometimes it's charging, sometimes not.
You changed the VR and the problem is still the same.
1. I would check if there's voltage on the IGN side of the VR connector. If that voltage drops, the VR stops working so the alternator is not charging. The truck runs on the battery which explains the needle going negative.
2. Next step is voltage on the F terminal on the VR side and on the F terminal on the alternator side. No voltage = no charging. Same story as above.
3. Check your +B cable on the alternator for bad connection/corrosion.

Rudi