Voltage regulator?
 

My 86 4runner 22RE is having random voltage voltage fluctuations. The alternator tests good at the part store, so is there a voltage regulator that might be bad? Any other suggestions?

Voltage is regulated by the reading (voltage) near the battery. If there is a bad, dirty, or frayed wire between the read point and regulator you can have problems with a alternator that bench tested OK.

Check the wire, and fusible links..

Yep.
"S" wire is what senses the voltage near battery. It is spliced to "B" alt-to-batt wire near the battery

Here's what and where to check:
https://www.yotatech.com/forums/f199...l#post52094780

Tested at the battery terminals with the engine running. 12v with random drops as low as 4v. Any electrical at all, lights, heater, radio drops voltage to 10-11.5v. I'm not e even sure there is an independent voltage regulator in the truck,or where it would be located....meanwhile, searching for bad wires, but some ˟˟˟˟tard did some bull˟˟˟˟ wiring on it before I got it.

Measured volts as I suggested at points here? https://www.yotatech.com/forums/f199...l#post52094780
Measure with engine off, with IG on, with engine running and report back.
Regulator is built into the alternator. Like Co says and I say, it gets feedback from "s" wire.

report
 

Engine off: 12.17 IG on:12.4 engine running:12.1 headlights on, engine running: 11.8. It fluctuates while driving with rpm's. From 13+ to 10 v, according to the after market voltmeter gauge I installed. Also just discovered today; a power steering leak that appears to be dripping on the alternator....thanks for your input so far, guys.

OK.Those are Battery voltages correct? Those readings are too low.
Yes, the power steering leak on alternator may be keeping it from working properly. Try fixing the leak*, cleaning and drying the alternator and try again.

*I had a P.S. leak which fortunately was just from "sweating" low-pressure hose. Was easy to fix. I just bought P.S. hose from NAPA.

Sounds like an alternator problem or slipping belt to me. You should be about 13 to 13.5 at the battery with the engine running.

my power steering leak was the plunger on the left side, has a snap ring and o ring in it. It dripped straight on the alternator and killed it as well as the lower radiator hose and elbow just above it. (Atf will eat regular rubber hose and belts)

13.5 to 15.1V
https://www.yotatech.com/forums/f199...l#post52094780

13.9-15.1v
http://web.archive.org/web/201102051.../2onvehicl.pdf
A little lower when hot.

Hey, i was in range.:)

I don't think I've ever had an alternator put out 15v.

regardless, his isn't putting out enough