scope103

https://www.yotatech.com/forums/f116...ng-fix-213466/

Okay, I'm going to guess you never had the old alternator tested. Here's to hoping the new one is good (so we can get you running), AND the old one was good too (so we have a place to look for the problem.)

First, you'll need to replace the 80amp fuse. Next, I assume you've put your multimeter on the large stud of alternator while running. I assume you're not getting around 14.1v, and instead are getting battery voltage (around 12.6v).

There are three regular-sized wires to the other plug. You should be able to back-probe it, but these tests are key-on, engine-off, so you can unplug it. The White (Sense) wire should have 12v with key-on or key-off. The Red (Ignition) should have 12v with key-on. The Yellow (Alt) should have continuity to ground when the alternator is not turning.

This should be obvious, but the ground of the Alternator is through the case. Apparently, some folks like a good-lookin' engine bay, so they get the alternator bracket(s) powder coated, and wonder why the alternator doesn't work. Probably doesn't apply to you.

RAD4Runner

Did you measure "IG" and "S" voltages like I suggested earlier? ^^^
How charging system works AND suggested test points are discussed here.

Yes, basic hand tools, not brute force... heh-heh
The terminals FL module is screwed in. You need to undo fuse block mounting to inner fender and access form the bottom.

green2man0

Thanks I just figured out the 80a link....found the screws to late....have one ordered from Toyota, it should be in tomorrow morning...so I'll pick that up at 8-9am tomorrow. I'll test the wires from the alternator plug for voltage....Is that the last things to possibly fix...I mean that's the whole charging system if my reading of the diagrams are correct.

green2man0

So tell me if this is right...I'm looking at the haynes wiring diagrams and trying to trace the wires for testing tomorrow.

White: Goes from the alternator to the 80A fusible link in the fuse box and then to the battery
Red: Goes from the alternator to the 15A engine fuse in the fuse box, then to the ignition switch and to the 40A fusible link in the fuse box, then to the 80A fusible link and to the battery
Yellow: Goes from the alternator to the 7.5A charge fuse in the fuse box (then I lose it, it says from combination meter/from emission control computer/from "IGN" fuse)

scope103

Close, but not quite. Unless you plan on taking the entire harness apart, WHERE is a wire goes isn't as important as what voltage you find on it.

The yellow wire ("L") goes to the Alt light, and the other side of the Alt light has 12v through the IGN fuse. When the alternator is not producing output, the L terminal is grounded, lighting the Alt light. When producing output, the L terminal goes to 12 or 14v, so the Alt light has the same voltage on each side, and doesn't light. That terminal is just for an indicator and the alternator will work with it disconnected. With it disconnected, the terminal should be at ground with the alternator not turning, and the wire should be at 12v (through the alt light) with key-on.

My EWD (for a '94) shows the White ("S") wire going to the 40A AMI fuse then to the 80A ALT fuse, but that doesn't matter. It's a "direct" connection to the battery; if it doesn't have 12v on it the connection is broken.

I have the same series of connections for the red ("IG") terminal, but again, all that matters is that it has 12v with key-on, nothing with key-off.

green2man0

Gotcha...I'll get that fusible link in, test the wires, then focus on the one that's not doing its job.
Thanks

green2man0

Ok new fusible link installed
White wire Key on engine off is 12v
Red wire Key on is .1v
Yellow ground wire key on is 11.1v

So something in the red or yellow wire...where should I check now???

green2man0

OK I think I got it...
I went through the driver side kick panel fuse box and found some inconsistencies. It was missing some fuses and others weren't the right amperage. I pulled all of them and started over based on the diagram on the kick panel. Once all the fuses were the correct amperage and in the correct space, I rechecked the voltage on the alternator wires and everything checked normal. The battery was low so while doing this I popped the trickle charger on so I'd have enough juice to fire it up. Cranked it over and fired right up. I put my multimeter on the battery and was getting 14.89 volts to start, after idling/warming up and getting the battery topped off it went down in voltage a bit, cycling between 13.9 and 14.2 volts. I'm letting it sit now for 20-30 min and will check if the battery voltage settles around 12.4-12.6ish and I'll try and refire after everything check out normal.

scope103

If fuse #1 in J/B 1 http://web.archive.org/web/201204170.../2powersou.pdf ("Engine") is missing, the alternator will not produce output, because there will be no voltage on the red wire ("IGN").

Good that your diagnostic skills tracked it down!

GO_BLUE!

I'm just spitballing here but all summer long I've had a small parasitic drain on my battery - -

Come to find out it was the cap.. the plastic cap... covering the positive post on the alternator... touching the metal tube of the dipstick of my '92 3VZE. Once I took the cap off I could see burn marks on the plastic where electricity had grounded to the tube.

It's helpful to run your hands along the wire from the alternator to the battery to check for any damage. Then the wire from the battery to the starter. Check your grounds from the neg post of your battery to the wall of your engine bay & block, and there is a small ground from your engine fuse box to the wall of your engine bay just behind the fuse box. Also replace the wire from the battery to the fusebox with 6g wire or bigger (see the write-ups on here). If none of that solves your problem, then you gotta start tearing things apart looking for a short. My truck is 25 years old now and the wires are brittle, especially the wiring harness underneath the intake plenium on the driver's side. The protective coating is completely gone.

If you're inside the truck, start with the stereo and/or any aftermarket accessories that may have been wired-in years ago with electrical tape. Also the rear window circuit board (raises/lowers the rear window & rear washer) is known to go bad. Another idea is to replace all your fuses in the interior fusebox.. even if they look good... because sometimes looks can be deceiving. The wires to your power windows & locks can get pinched & damaged from the doors to the dash, so open your front doors and pull the protective boot off and look for damaged wires.

That's about all I got... from my experiences. Good luck.