How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Toyota Service Your Own Question
Toyota Service
Toyota Service, Toyota Expert
Category: Toyota
Satisfied Customers: 4805
Experience:  30+ Yrs of auto experience, Award Winning Svc. Manager; Just Answer Customer's Choice Award Winner
14892859
Type Your Toyota Question Here...
Toyota Service is online now
A new question is answered every 9 seconds

My truck (1980 Toyota )won't charge the battery. New alt,

Customer Question

My truck (1980 Toyota )won't charge the battery. New alt, new voltage regulator, new battery. Any suggestions?
Submitted: 1 year ago.
Category: Toyota
Expert:  Amedee replied 1 year ago.

Hello and welcome! My name is ***** ***** I can assist you with your question. Can I start by getting your VIN? Thank you!

Customer: replied 1 year ago.
RN37019648 is my VIN
Expert:  Amedee replied 1 year ago.

That vin does not come up. Can you double check please?

Customer: replied 1 year ago.
That's what it says on the plate inside my drivers door. The only difference is there is a dash between the RN and the numbers. I gave the same # ***** my insurance company and they had no problems.
Expert:  Amedee replied 1 year ago.

Ok, thank you for checking that. I wont be able to help you. I will leave this open as another expert may be able to assist.

Expert:  Ted Ritter replied 1 year ago.

Hello,

do you have battery voltage to the large wire attached to the alternator?

Customer: replied 1 year ago.
I do
Expert:  Ted Ritter replied 1 year ago.

The voltage regulator has 4 wires, three go to the alternator and one comes from the alternator fuse as far as I can tell, I have an old diagram but not sure of it's accuracy, the single wire coming from the fuse should be black, with the key on there should be voltage of about 12 volts.

One of the three wires between the regulator and the alternator should also show 12 volts.

Customer: replied 1 year ago.
The voltage regulator has 6 wires (55 amp type) and the only fuse that would be related is the "engine" fuse(15 amp) and that goes to the regulator.
Customer: replied 1 year ago.
the fuse is not blown
Expert:  Ted Ritter replied 1 year ago.

Ok, I just don't have much info anymore on a truck of this year so I'm going to have to opt out at this time, maybe another expert can assist with this, please do not rate my answer so another expert can get involved.

Expert:  Toyota Service replied 1 year ago.

Hello. Different expert here. Many years ago I had this exact same issue in the shop. After testing 3 different alternators, and replacement of 4 new voltage regulators, we determined that neither of those was the issue. What we did find, after many hours of testing, was a bad diode in the fuse panel. We replaced the fuse box under the dash and the problem was solved. Hopefully, this is what your problem is.

Customer: replied 1 year ago.
Assuming this is the problem, how do I test that?
Expert:  Toyota Service replied 1 year ago.

You need to take the fuse panel out and take it apart. Inside you will find a diode. With a multi-meter capable of testing diodes, test both ways. Power should flow one way, but not the other.

Customer: replied 1 year ago.
a bad one will have either power able to flow both ways or no power flow at all? This diode, is it the only one? If there are multiple diodes I'll check the one on the "engine fuse" circuit as that is the only circuit that deals with the charging system on the fuse box
Expert:  Toyota Service replied 1 year ago.

diodes prevent power from flowing one way, but will permit power to flow the opposite way.

Customer: replied 1 year ago.
I'll check it out when I get home
Expert:  Toyota Service replied 1 year ago.

Ok. Thanks for the quick replies

Customer: replied 1 year ago.
I'm off at 11 EST so you won't hear from me until tomorrow. Fingers crossed
Expert:  Toyota Service replied 1 year ago.

Copy that. No worries. I will be back online tomorrow at 3 PM EST

Customer: replied 1 year ago.
There are no diodes in the fuse box. Only wires that go into fuse terminals.
Expert:  Toyota Service replied 1 year ago.

Then your diode is inline in the wire harness. My schematics only go back to 1984; the diode has to be there to keep voltage from flowing both ways; there is not much difference between a 1984 and a 1980

Customer: replied 1 year ago.
Again I'll have to look tonight or in the morning. I started tearing the dash apart and didn't get too far into it because of the speedo cable
Expert:  Toyota Service replied 1 year ago.

OK

Customer: replied 1 year ago.
After tearing the dash apart completely there is no good news. I thought there would be a relay, come to find out, that is only on cold weather models. This is a SoCal special complete with a 1979 emissions computer. I started tearing into wire bundles and tracing wires. I checked the schematic and the only diodes in the charging system are in the alternator.
Expert:  Toyota Service replied 1 year ago.

Southern California special? Rare indeed. That is a totally different schematic....and I do not have that one. Apologies.

Customer: replied 1 year ago.
That's not the official monicker but it doesn't have the beefed up charging system and it has the emissions computer. I still have to finish stripping the wire bundle then I'll start shooting wites
Expert:  Toyota Service replied 1 year ago.

ok. This sounds like you have a wire issue between the alt/voltage regulator/charge light (or...a bad ground at the regulator)

Customer: replied 1 year ago.
I went back through my schematics and noticed something a little weird. The year truck that I have came with either a 40 amp alternator and ext reg or a 55 amp alternator and reg. The circuit for the 55 amp system has the relay I mentioned earlier to control the charge light. My system doesn't have the relay so it is the 40 amp system. I currently have the 55 amp hardware installed. Could that be the problem since there is no relay to tell the alternator to charge it never charges?
Expert:  Toyota Service replied 1 year ago.

Absolutely.