aldom92

I recently bought an 86 4runner with a 22re. When I bought it, the battery was bad, so I purchased a new one. More recently, I was driving down the highway, and the vehicle just lost power and died. When I tried to start it back up, the battery was dead. I automatically assumed the alternator was bad. I took it off and took it to my local autozone, where they confirmed it was bad, so I bought a new (refurbished) one.

After installing it, I now have my alt temp, charge, and brake lights staying on on my dash. It had not done this before. I searched the yotatech forums, and those three lights seem to indicate that the alternator is bad.

The battery measures around 12.8v with the vehicle off. When I turn it on, it slowly rises to just below 15v. Turning on the headlights, it goes back down to around 13v and stays there even after turning the headlights back off.

Is it likely that the alternator I bought at autozone is bad or could it be something else?

thanks

wyoming9

iTrader: (1)

From your measurements it seems like your system is working correct.

I would take the plug off the back of the alternator give that a good cleaning with contact cleaner.

I have seen this problem so many times

see if that fixes your issue

perhaps in the swapping of the alternators you may have broke the yellow wire going to the charge light at the plug.

The wires get brittle after all this time from the thermal cycling being below the exhaust manifold.

SoCal4Running

Check the fuses in the divers side kick panel.

aldom92

All the fuses under the hood and behind the kick panel are good.

I took the connector off and sprayed the front of it with cleaner, plugged it back in, and no change. Lights were still on. Decided to take it off again and spray the back this time where the wires are just barely exposed, plugged it back in, and the lights were gone.

I find it so strange that that did it. Thanks for all your help

aldom92

Apparently, I spoke too soon. Just started her right back up again, and the lights are back. Unplugged it from the back and tried spraying it again (hoped it would work) and plugged it back in, and lights are still there.

Any ideas?

aldom92

I took the alternator and battery to get tested at my local autozone today. According to the autozone dude, both the alternator and the battery are good. The lights are still on, though.

Hadmatt54

I'd confirm that they did a load test on your battery over time based on the amp hour output of the battery and not just a voltmeter check. A battery can test the very best in a non loaded state and then go to sh** when a load is put on it.
Your alt warning light comes on as soon as the key is in the start or run position to let you know that that circuit is functioning properly. The "L" terminal on the back of your alternator connects to transistor tr3 in the regulator which is switched on by the internal regulator sensor when the vehicle is not running. This transistor provides a path to ground so that the alt. warning light is lit. Also tied to this is your brake light and if your truck is an auto the transmission oil temp light. These two lights are also lit at this time. Once the coils in the alt are excited and the alt starts charging the sensor detects this and opens tr3, which puts all the lights out.
If these lights are on then you have a :-
Loose or worn drive belt
Defective battery or connections
Blown fuse or fusible link
Defective relay, regulator or alternator
Defective wiring.
If the internal regulator does not detect voltage on either the "B" or the "S" terminals it will turn on the light. If it detects too much or not enough voltage on term "P" (approx 14.5v) it will turn on the light.
So first I'd verify the tests that Autozone did on your alternator and battery. If they load tested the battery and verified that not only is the alternator charging, but that the internal voltage regulator is working properly, then I'd look at the connections again.
Maybe the female spade on the "S" (generally solid white or white/yellow) is spread and not making a good connection. These terminals can all be removed from the plug, generally a set of jewellers flat blade screwdrivers work pretty good. The "L" spade is okay, because if it wasn't then your light would not work at all. If these first things check out, then it is continuity checks on the "S" wire, fusible links etc.
If you really want to understand how the Toyota charging system works, this is a great resource
http://www.autoshop101.com/forms/h8.pdf

RAD4Runner

Actually, a broken "L" wire would prevent charge & brake error lights from coming on, unless it is shorted to ground.
Agree with this and what Hadmatt54 said ^^^

White "B" wire (heavy gauge) to the 80amp fuse is the battery charging wire.
From FSM:
With engine from idle to 2000RPM, Voltages at B should be:
13.9 to 15.1 V @25°C (77°F)
13.5 - 14.3V @115°C (239°F)

If lower than this range, make sure "IG" connection from engine fuse is good. and you read 12V at IG.

I have schematic, and voltages you're supposed to read at test points "L", "B ", "S", and "IG", in my post here.

aldom92

I hadn't driven the 4runner in a while cus I was scared it would leave me stranded or something, but today, I was feeling dangerous and decided to try to take it to work. After about 15-20 miles, the lights turned off. Thanks for all the help

RAD4Runner

Good to know you got it working. Still good to monitor voltages mentioned above ^^^. If you don't have a digital voltmeter installed, one of these cigarette lighter socket volt-meters would be good. But pLease keep you eye on the road .