ST165 alternator not going past 12 volts

Mateo

Member
My battery died in ST165 and I thought it was the alternator, which I've replaced twice with a Desmo unit. I've also replaced the battery twice, first time was a die hard Advanced Auto one but it was too tall so I swapped it for a Optima red top along with the terminals but still no increase in power. I've also tested the alternator for ground and it has that as well, but its just not giving enough power even when being revved. Any help would be appreciated.
 

Mateo

Member
RedCelicaTRD":372ta863 said:
Are you measuring the voltage at the battery or directly off the alternator?

I've tested both. Battery right now is around 11.9 volts and doesn't spike at all during idle but the alternator does about the exact same voltage when you measure off the 10mm bolt that is above the 3 prong connector.
 

Mateo

Member
Update: tested everything on the 3-wire alternator connector, colors aren't really useful in my case because the wires have been messed with so much.

Left vertical connector:
Volts to positive : 11.8 V
Volts to negative: 0.3
Resistance to positive: 0
Resistance to negative: 0.9
OHMs to negative: ~285-300

Middle flat connector
Volts to positive: 0.9
Volts to negative: 11.8
Resistance to positive: 0.9
OHMs to positive: 100

Right vertical connector:
Volts to positive: 0.3
Volts to negative: 11.8
No OHMs or resistance, assuming this is the ignition, also the battery wire on the alternator to the battery reads about the same voltage so no major voltage drop there.

I'm still very much a beginner to car electronics so if someone could dumb this down to me that would help a ton.
 

RedCelicaTRD

Moderator
How do you have your meter setup? Since it's not too complicated of a circuit, and we want to know what voltage is at the connecter, you should have the black lead to ground. Sticking it on the negative battery terminal is ok.

I assume you have the connector pulled and are testing the wiring on the connector? Are you testing these with the ignition turned on or off (with the car not running)?

If we are looking at the alternator from the drivers side looking into the alternator connector here's what the three terminals do:

LH Vertical: "IG" or ignition. This is power from the ignition switch to "turn on" the alternator. With the switch on you should measure battery voltage at the connector. If you don't, there is a fuse that should be checked and then wiring.
Middle flat: "S" or sense. This is the feedback from the battery that lets the alternator know how it's doing. If the voltage is too low it will crank out more, too high it will output less.
RH Vertical: "L" or lamp. One the alternator output is low enough this allows the dash light to come one. We won't worry about it right now.

With the negative lead on the battery, test the voltage at the wiring harness connector. Mainly look at the S and then IG with the ignition switch on and off. Check that the wiring is in good shape and the copper connectors look clean and have a wear pattern where they have been making contact.

Also, just because you got a reman alternator doesn't mean it was actually rebuilt. The reman auto parts business is pretty shady. I've seen people go through multiple "reman" alternators until they get one that works.


More reading:
https://www.electricalrebuilders.org/er ... nators.pdf
 

RedCelicaTRD

Moderator
Someone also has posted a 1988 Toyota alternator testing guide over at the ol' CelicaTech.

http://www.celicatech.com/bgbonline/89t ... ndenso.pdf

The current testing they are doing is a bit more complex and needs a pretty good amp meter to do. However, they do show how to do the "Full Field" test which can be helpful. This basically bypasses the internal regulator and tells the alternator to put out max voltage. Alternators can't put out too much voltage, so a quick removal of the limit for testing isn't a big deal. This will help tell you if the internal regulator is bad or if the alternator is simply not capable of outputting the voltage that it should.
 

Mateo

Member
RedCelicaTRD":384pzx9a said:
Someone also has posted a 1988 Toyota alternator testing guide over at the ol' CelicaTech.

http://www.celicatech.com/bgbonline/89t ... ndenso.pdf

The current testing they are doing is a bit more complex and needs a pretty good amp meter to do. However, they do show how to do the "Full Field" test which can be helpful. This basically bypasses the internal regulator and tells the alternator to put out max voltage. Alternators can't put out too much voltage, so a quick removal of the limit for testing isn't a big deal. This will help tell you if the internal regulator is bad or if the alternator is simply not capable of outputting the voltage that it should.


I actually managed to find a printout of the electrical diagram for the alternator, which I'll be testing tonight. The "F" terminal which is a hole on the cover of the alternator you can stick a screwdriver in it and ground it to the case and when you do that the alternator will output max voltage, so a good way to test the alternator. My current theory is that the sensing cable is having voltage drop somewhere, which I'll test. Also never heard of Celicatech, will definitely look into that. I also screwed up the ohms reading because i did it while the car was running lol
 

Mateo

Member
RedCelicaTRD":2zih06xh said:
Someone also has posted a 1988 Toyota alternator testing guide over at the ol' CelicaTech.

http://www.celicatech.com/bgbonline/89t ... ndenso.pdf

The current testing they are doing is a bit more complex and needs a pretty good amp meter to do. However, they do show how to do the "Full Field" test which can be helpful. This basically bypasses the internal regulator and tells the alternator to put out max voltage. Alternators can't put out too much voltage, so a quick removal of the limit for testing isn't a big deal. This will help tell you if the internal regulator is bad or if the alternator is simply not capable of outputting the voltage that it should.


I just tested the 'F' terminal and grounded it with a screwdriver and that is supposed to output max voltage, but I only got about 1/2 a volt more. Did Napa sell me 2 faulty alternators?
 

Mateo

Member
Solved it...

Previous owner jammed a metal clip into the charging fuse in the driver fusebox and ruined the port and only works with that clip in... Not sure why they didn't just wire it in like a normal person, I disconnected it to wire in my wideband properly. The fuse can't make a proper connection without it. 99% of my issues are just the previous owners janky wiring
 

Roreri

Active member
Man I'm glad for you. I was worried that there was some gremlin in the wiring that was killing your alternators.

I'm counting my blessings. Everything the previous owner of mine did seems to have been wired nicely.
 

Mateo

Member
Yeah my previous owner had the wastegate actuator held in with zip ties... That should tell you enough about the state my car was in when I bought it. Sounds like you lucked out and it was maintained nicely, good luck with your car.
 
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