A month ago my ABS and battery light came on with a constant on light. My cheapo multimeter showed 10volt so i bought a remanufacture Denso Alternator. The ABS light went off and the battery light would turn off and on since then. My suspicion was that the battery (optima red) was weakened and would eventually restore itself. After the alternator was installed i had autozone test it and the battery was 12.4x and the alternator was 14.4.

I also replaced the black (-) battery cable to the engine block after the install.

Yesterday, my lights started to flicker so I tested the battery and Alternator with my new digital multimeter. Wow! 16.6v was the high but no lower than 15v. My thought is that the regulator was faulty and not replaced when they rebuilt the alternator. I pulled the alt and drove it to autozone and it tested good at 14.4v.

Could it be faulty when hot, but good when cold? Is that possible. Continuity is good.

 

How long had you been driving till the lights started to flicker??

That would pretty much answer your own question.

You might say something when you take it to be tested next time that it seems to be heat related.

But seriously if you have a meter don`t you trust yourself.

underload as high as 15VDC is not good for the life of your battery.

***!! when installing a new/rebuilt alternator your battery should be up to full charge.:jessica::jessica:

 

the battery was 12.4 - 12.6 when the reman Alt went in. last night while the output was 16v, the battery was 13v w/engine off. this morning stone cold, the battery was 12.4v.

The lights just started flickering last night which is why I pulled out the multimeter again. I'm thinking this may well have been the reason the alternator was sent to be rebuilt in the first place. They just didn't catch the problem when it went thru QC.

Edit: I ordered a new TYC alternator from rockauto.com for $114 shipped. Did you know these alternators have a lifetime warranty? That says a lot about their confidence in their alternator.

 

Update:

The new TYC alternator arrived and got installed this weekend. While I was in there, I made a new Alt to fuse box cable using 4ga battery cable. When I tested the continuity of the old one it showed some resistance so it made sense to replace it. I picked up a 38" battery cable 4ga and copper lugs with 1/4" holes for a total of $12 at Autozone. Cut off the ends and crimped/soldered the copper lugs onto the cable. So now the alternator can supply ample current even at idle.

What I noticed with this new TYC Alternator is that even at idle 700rpm with the headlights, wipers, HID spot lights and radio on, the alternator was putting out 14.5v. I know the old alternator would drop into the 13v range and the lights would dim.

 

Your now right where you should be for alternator charging output. What did that wire read for resistance? Resistance tests are kind of meaningless with a wire that size. A better test would be a voltage drop. Or test your available voltage at either ends of the wire. If you have 14.5 at one end and 12.0 at the other end under load. You now know that you have a high resistance in that wire and you are losing voltage across it.

 

Edit: Sorry about that. I was a few steps beyond your comment above. The wimpy 6ga wire that bridged the alternator and fuse box had corroded ends so I just wanted to give it some more capacity since I had the alternator off the truck anyway. What I was referring to below was the signal wire from the alternator which was broken.

On the white signal wire, There was zero resistance. I tore into the harness and found a break in the wire. It was in an odd place where it couldnt flex. It was green too. Must have been there from the factory. Its fixed now. I just need a few rolls of electrical tape to put it all back together again.

What does the white wire do anyway?

 

Where does it go?

 

The white wire (16ga) goes from the alternator to the plug at the base of fuse box. It's one of the 3 alternator wires. (Red, yellow and white)

 

It will be the sense wire for the alternator

 

Yes, agree with fanaticakilla... normal operating condition output voltage from 13.5V to 14.5V. Outside of that you have fault condition.

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B: Thick (awg4 wire) is battery charging wire.
S: 16awg wire is to sense battery voltage
IG: red wire is to provide field current to alt. regulator adjust this to control output voltage
L: yellow wire is charge light. When output voltage

Normal operating condition (output 13.5V to 14.5V), "L" output is high or 12V. Fault condition, "L" will go low providing ground to negative side of charge light.


Because there is positive voltage (steady 12V when ignition on) on other side of charge light, light will come on.
If you have poor battery terminal contact (i.e., corrosion) and you have momentary loss of connection, it could lead to intermittent (split second) over-charge/under charge conditions and trigger "L" to go low. So make sure you have clean and secure connections.

Unfortunately, for some stupid reason, Toyota lets this alternator "L" fault output to also ground negative side of brake error light (at least on earlier gens), so it creates misleading fault indication.

Best of luck.

 

Glad you found your problem and got it fixed. I'll have to remember that RAD4Runner is the guy in the know when it comes to alternator/electronics. I like the diagrams and detailed explanation. Thanks!

 

"Green"? you mean green insulation on wire? or green from corrosion? Found Which wire it is on the schematic?




Tnx, Sir 98SR54RUNNER! Just trying to give back to forum that helped me find Ruby Tuesday

Hey guys, I have found this really handy, low-cost aid to monitor charging system. Would tell you if charging system is significantly "off". Ideal of course is to measure batt voltage directly but this is good enuf for non-intrusive monitoring of charge voltage. Good conversation piece, too- LOL!

 

Where the insulation was broken, the copper wires were corroded green on the white wire.

help me understand the outcome if the white wire is cut and non functional.

So other than the idiot light, does the white wire control anything else like the regulator output?

 

You're talking about the AWG 16 white wire? That's the "sense" wire. If broken that would make alternator think battery voltage sis zero meaning discharged so will try to keep on charging, even if battery is already fully-charged. Could cause overcharging. Not sure of final result.. maybe overheated battery.

 

So theoretically, if the alternator is perpetually trying to charge the battery it could add drag to engine and cause mpg to worsen?

Ive been curious why my mpg has dropped from 20 to 16 since Nov. this next tank of gas will let me know.

 

Possibly. It would keep charge voltage up at 14.5V (IF regulator is working normally), when it should already be lower. That's why cigarette lighter volt-meter, is handy.

Glad you found the problem. Regards.

 

How tight you got your alternator belt? That could do er too

 

Well this could explain my drop in mpg over the past 6months. Looks like my truck could be back to 21 mpg. Normally when the gas gauge needle reaches the full line, i have gone 30 miles. Now I am at 40 miles when the needle hits the full line. A 30% improvement in mileage?? That would be a nice surprise.

I will post the results when I empty the tank.

Thanks for everyone's help.