Hi, I bought an 1986 4runner, 4y engine with carburetor. Yesterday the battery symbol in the dash came up.

I checked the voltage and it is 12,6v. Even less when running, so the battery is not charging.

The alternator belt is fine, the alt itself has four wires on it : a single white one and a plug with a two blue and a green one.

I checked the fuses in the box under the hood, they are ok. Are there more fuses?

I'd like to check the alternator, I already checked the white cable against ground from the battery and I get 3-7v depending on the engine speed.
Can you tell me what to check? Thanks!

 

Sorry, odd engine and alternator wiring. Got schematic of your charging system?
We'll go from there.

 

Thanks for your reply. I am in Australia, but the engine is indeed very rare. I think it might be from the Hilux?
The Vin starts with yn63...I was hoping you could tell me something about the car

 

Like Rad4Runner, I don't recognize those wire colors. Do alternators run backwards south of the Equator? (Sorry, bad joke ....) Also, I don't know much at all about the '80s vintage 4runners, though they are "mostly" the same as the later models.

The "fat" single wire from the alternator is the output; it should connect directly to the battery through a big (usually 80amp) fuse. The fact that the voltage on the alternator is different than the voltage on the battery suggests that you have a bad connection on that wire. (But if the 80amp fuse is open nothing should get power; the truck shouldn't run). That wire (and therefore the battery) should be at about 14.1v when running, and shouldn't vary with engine speed (or much of anything else; it has a regulator).

The other three wires are Ig (ignition, 12v with key-on, provides field excitation) S (sense, connected directly to the fuse box, so it should be at battery voltage all the time) and L (alternator Light, pulled to ground with the alternator not producing power, pulled up to 12-14v with the alternator working. The other side of the alt light connects to 12v, so when the alternator is running there is 12v on both sides of the light and it goes out).

You could remove the plug and check for voltages on the plug with key on and off. You could check for continuity back to the battery on the fat wire. The 3-7v on the alternator output is, of course, too low. You probably need to replace the alternator, but given that the fat wire is at the wrong voltage you may have an interesting wiring problem.

Good luck!

 

Ok, I found out that the battery is charging sometimes, 14v on the battery. Unfortunately that happens only for 1-2 minutes every hour..

I took out the alternator, I could spin it without any resistance... Is that OK? Check this picture of the brushes, I think I should get new ones?
http://abload.de/img/hro50.jpg

 

Since you have the alternator out, I'd take it down to the local auto parts store and have them test it. In the US, at least, most parts stores can test it in a couple of minutes and tell you whether it's working or not.

I don't think the alternator should have much resistance to spinning when the field winding is not excited. Under those conditions it's pretty much just a shaft and rotor on bearings. I'd be more worried if it did have significant resistance to turning.