Having a charging issue, 87 pickup. Put brand new alternator in, no luck? Traced the white alt wire all the way from the alt to fuse block, and it's in good shape and not frayed or burnt up. Brand new 80 amp fuse, new 7.5 fuse. Wire from fuse to battery is new.

What am I missing? Any other wire off the alternator I need the check, is there a power wire to turn it on?

I know my drag car has a toggle to turn my small block alt on and off, do these toyotas have a wire to do the same?

 

Yes the alternator gets excited through the other plug in the back without looking I forget the color.

These plugs do tend to corrode

Poor grounds will also cause a no charge condition

If it is a reman or new alternator good chance it might be bad out of the box

You started with a charged battery ??

 

I actually bought the truck 2 weeks ago and it's been like that since I bought it. I tried looking through a manual, but trying to understand it is like trying to build a spaceship

 

These trucks use the idiot light as the exciter circuit , so if your truck has one, check to see it is working.

 

I don't recall seeing the CEL whenever I ran the truck last, I can't start it right now I'm waiting for gaskets for the 32/36,

Speaking of that, this's truck has been converted to carb, so if imagine there would be a CEL. Idk I'm kinda confused what u mean

 

When you turn the key on before cranking, the charge light will come on and go off when the engine starts. If your truck has the gauge cluster with a volt meter it won't have the light. The light coming on is what starts the charging system working . It might be the bulb being burnt out causing the problem. You can jump 12v to the 7.5 fuse in the fuse box under the hood with the engine running the charging system should work. If the exciter circuit is the problem it will charge until the engine is turned off.

 

First, how do you know you have a charging problem? With the truck running, you should have about 14.1v (temperature dependent) right at the battery. If you have about 12.6v, that's a charged battery that is not chargING. If less than 12.6v, I'm not sure how you started it.

(Note that you have to check for voltages; just looking for "frayed" wires is not enough. You have to use a multimeter to diagnose an electrical problem.)

There are two connectors on the alternator; the the fat "battery" wire that goes straight to the 80Amp fuse and carries the charging current, and a 3-wire connector that plugs in. The three wires (Red-excitation, White-Sense, Yellow - warning Light) provide the excitation voltage (switched by the key), sense the voltage for the regulator (right to the fuse box) and light the "alt" light. You need them all.

No, you're thinking of an old "3-wire" alternator. If the bulb in the idiot light burns out, you're dead in the water. Fortunately, our trucks use a "4-wire" system.

edit: oops! After looking at a picture of an alternator for an '87, I can't tell if the plug has 2 (3-wire alternator) or 3 (4-wire) connections. If it has 2, then swampfox is correct, and a burned-out bulb in the alt light will shut off the alternator. But the test is the same; if you don't have battery voltage on both pins, then you've found the problem. And if that's the case, I'd check the bulb before horsing around with a bypass.

 

The battery has 12.65 volts and it starts just fine, checking voltage at the battery while running it stays the same 12.6

Can I put a toggle in the cab, and run power from that to the red or white signal wires, to turn the alt on or off?

I'm kinda stumped, all the connections are clean and tight, the main power from alt to 80 amp fuse block is hooked up and tight connections, no corrosion. I'm guessing maybe it's ignition related but it's just a mud truck, and if I can get around it without causing a fire lol. Only thing I haven't checked is the voltage right at the alt white post

I have no problem turning the alt signal on by a toggle if it can safely be done

 

I don't know, can you?

IF you KNEW (for sure) that your only problem was in the ignition switch, and you were too cheap to fix it correctly, you could use a toggle switch. Except that it isn't the ignition switch (without IG2 nothing would run). It's somewhere else.

You need to use your multimeter (I know you have one; you're giving decimal voltages) on the red and white wires, AND on the B terminal (the big stud with the fat wire). Red and white should both have battery voltage (12.6 in your case). If they have that, and the B terminal has 14.1, you know the fat wire is not good. If the B terminal is 12.6, your alternator is dead. Schlep it down to Autozone/O'Reilly's/Napa for a free test to be sure. Then plunk down your $110 (or $75 at RockAuto) to replace it.

Good. Your mother will be proud. But absolutely filthy, floppy cables will carry electricity just fine. (And clean ones might not!) That's why you have a multimeter. You have an electrical problem; a bottle of windex will not help you. A $5.99 multimeter will find the problem in just a few minutes.

Good luck!

 

Thanks for the help and being patient. I know it's frustrating dealing with noobs, and wiring is my weakness. Can't start the truck because the carb is off.

I have 12.65 volts at the big white alt post (with the truck off, so the main big white to B terminal is getting juice).

I turned the ignition on, not running, the white wire on the alt plug is getting 12.45, the red is getting 0.

So it's either a bad alt, or it's because the red wire has no voltage. Is the red wire what triggers the alt on? And if so where does it go from so I can investigate further.

Thank you for your help so far.

 

The white is "sense", so 12.45 is good, the red is excitation, with key-on 0 volts means that wire is not connected back to IG2.

First, do you NOT have a yellow wire (or a third wire through that connector? If you don't, that means you have a 3-wire alternator and swampfox is correct. This is important because I believe that some 3-wire alternators MUST have some resistance in the excitation (red) wire, which is provided by the bulb in the ALT light. I just don't know in your case. So I don't know if you could safely wire 12v directly to the red wire. What I would do is work backwards through the bulb to see if you can find 12v with key-on. (initially, by checking the bulb!)

(Just so you know, on the more modern 4-wire alternators, the ALT light has 12v on one side with key-on, which is grounded through the yellow wire of the non-running alternator. Once the alternator spins up, it raises the yellow wire to 12v. The ALT light has 12v on each side so it doesn't light (no current)).

Remember that you can measure 12.65 volts through a teeny-tiny bit of wire, so I can't rule out the possibility that your big white isn't connected big enough, but for multimeter checking it has "passed."

It's going to be pretty hard to tell if any of these fixes will work without being able to spin the alternator.

 

how bout you just pull and bench test that alt instead of chasing could bee's. Since there's no carb n all...

 

It is a 4 wire alternator, I didn't check the yellow because you listed the white and red.

Right now I have no Alternator light, or any dash lighting for that matter. I need to check those fuses when I get to it, just wanted to start with the biggest known problem. I'll follow the red wire, and check stuff out when I get the truck started again.

I hate wiring. I'll test the alt this weekend

 

If it's been converted to a carb who knows what all has been done. Like mentioned, since you can't start it pull the alt and have it tested over at O'reilly Auto, AutoZone, NAPA, CarQuest, Advance Auto, even Pep Boys can probably do it and it's normally free. After that suspect a wiring problem.

 

Re: Toggle... Don't butcher a Toyota.

Pls see my sig for how charging system works on 86-88, and test points.

Summary:
Yes, 4-wire alt.
IG - red wire is Excitation. Should have 12V when Ignition switch is in ON position. If it doesn't, trace wiring until you see where you lost 12V.
S - white wire is Sense. Should be same as Batt voltage.
L - yellow wire is Charge Light. Alternator does NOT depend on it in order to generate electricity. It merely tells you when alt system is not putting out proper voltage.
B - Thick wire on post is alt output. This is where you should be monitoring voltage. Should be pretty much same as voltage at batt + post.

 

I am having same kinda problem just bought this Toyota but it's a 1990 3.4 swap brand-new battery got a new alternator in even tho I didn't need to checked all the wires grounds and plugs fuses seem good but my voltage meter says 12.6 when the truck not running and running and then the voltage start slowly dropping alternator is not charging battery I have no idea what's wrong

 

Should be same as First-gen MoreFunner. Take voltage checks at IG, S, L and B as described above.
Details here.