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Technical Alternator wiring issues

Discussion in 'The Hokey Ass Message Board' started by Grandpacharli, Aug 17, 2021.

    Joined: Aug 1, 2009
    Posts: 693

    from 94577

    Nope, that is not an effective '3 wire' alternator.
    That is a 1-wire alternator wearing the coat of a '3wire' alternator.
    Did it have a rubber plug on the #1 and #2 terminals when you purchased it?
    That would indicate it was converted to '1 wire'.
    Last edited: Aug 17, 2021
  2. brading
    Joined: Sep 9, 2019
    Posts: 478


    Think you right there Mike this more than likely to be a 1 wire alt to run it as a 3 wire you have to change the internal regulator as they are internally different.
  3. Grandpacharli
    Joined: Feb 17, 2020
    Posts: 27


    Hi Mike yes you are right . I’ve rigged it up no with the 1 wire on the back but still having the same issue .

    I may order another 3 wire alternator today . I just can’t see how 3 known good ones can do all the same thing . They all emit power until it’s hooked up to the truck. I just don’t get it.
  4. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,577

    Johnny Gee
    from Downey, Ca

    I helped a coworker with an off topic vehicle with charging issues. She took it to several shops, all replaced the alternator. I did some research on her type of equipment and found odd things as well when probing wiring. I took that alternator to an electrical repair shop. It was bad. They repaired the unit and BAM!, the vehicle charged again.
  5. junkman8888
    Joined: Jan 28, 2009
    Posts: 676


    Reading your original post you never mention if the charging circuit actually ever worked in the first place, in a later post you mention the "loom" is new, but does that mean the wiring harness for the entire pickup is new or just the alternator?, and oh by the way, was it wired correctly?
    What you need to do is stop looking for an easy fix, get a wiring diagram for your year pickup ( I say for "your year pickup" because the harness is wired differently every year), a wiring diagram for the alternator you're using (let's just say it's a 1972 alternator, get a wiring diagram for a vehicle that uses that year alternator), then mate the two.
    You are never going to fix this problem unless you go through the entire system, wire by wire.
    26 T Ford RPU likes this.
  6. KenC
    Joined: Sep 14, 2006
    Posts: 668


    it seems to me that your new loom has that wire connected to the wrong spot in the fuse/terminal block. It should connect to a key on hot term not the accessory section
  7. Mr48chev
    Joined: Dec 28, 2007
    Posts: 30,192


    I'm thinking his testing methods are blowing diodes. The least bit of arcing will blow a diode on some of them.

    Way back in the 60's one of my first experiences with working with an alternator was testing and repairing one that some old fart had changed on his early 60's car and then decided that he had to "polarize" it after he installed it by arcing the regulator as you did with a generator. I can't remember how many diodes were blown but it was a bunch. That was a real common thing around the mid 60's as you couldn't beat it into those guys heads that they absolutely did not do that with an alternator.
  8. Grandpacharli
    Joined: Feb 17, 2020
    Posts: 27


    So I built the truck around 2 years ago. New everything harnesses bay cables and all new ancillaries including the alternator . It’s run perfectly till this point. I have just put a brand new alternator 3 wire on after no luck with the previous of the shelf one. And still does the exact same thing so the alternator checks out okay because as I said it charges but not when you aply the power to truck. It just dies off ! Starting to loose it now
  9. KenC
    Joined: Sep 14, 2006
    Posts: 668


    Can you clarify what the red means? what wires are hooked where when it charges and what is changed to stop it????
  10. Grandpacharli
    Joined: Feb 17, 2020
    Posts: 27


    I’ve managed to solve that issue . The alternator I ran was a 3 wire before but the new one is a 1 wire . The exciter wire pulled constant power from the adjoined terminals pin 1 and 2 so it had constant power to the fuse panel.
  11. Grandpacharli
    Joined: Feb 17, 2020
    Posts: 27


    Another test I just done was to run the truck and run a cable from the power output on the back of the alternator to the separate battery and then a jumper cable from earth post to the alternator to see if it would charge that but it does the exact same thing .
  12. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 5,666


    Cut that link and wire it like it was designed to be. Terminal 1 should be wired through a small 12 volt bulb to the ignition terminal on the switch. Terminal 2 should go directly to the battery, not to the battery post on the back of the alternator. It is the "sense" terminal, and needs to know the voltage at the battery in order to charge it properly. If it can't reference the voltage at the battery then voltage drops through the system can result in a chronically undercharged battery, and shorter battery life. The large BAT lug can be connected to the starter or directly to the battery.
    26 T Ford RPU likes this.
  13. In your post above you said,"The alternator I ran was a 3 wire before but the new one is a 1 wire".

    If it's a 1 wire, why is it not wired as a 1 wire?
  14. MAD MIKE
    Joined: Aug 1, 2009
    Posts: 693

    from 94577

    I kinda read through the thread, and I kinda fell asleep reading it cause I'm running on 30mins of sleep in as many hours... again.

    For a true 3 wire alternator to work.
    BAT terminal can go to the battery directly, usually the starter solenoid lug is used as an easy way.

    #1 terminal('EXCITE') should go to the 'ALT' or 'GEN' lamp in the dash with a resistor running in parallel to allow the alternator to excite it. Also a diode should be in series to prevent backfeeding/draining issues.

    #2 terminal('SENSE') should go to the main bus of the electrical system. Older vehicles this was usually the horn relay. If you have a newer vehicle or a retrofitted/updated harness the fuse box main power feed bus is a batter place. This is for the alternator to 'sense'(monitor) SYSTEM voltage, if the voltage dips from load then the alternator can kick up the voltage to compensate. This is the best way.

    What lots of folks do is the #2 Sense wire gets bolted directly to the BAT terminal.
    This defeats the functionality of the Sense wire. Unless there is a large enough load to pull down the voltage at the BAT terminal, it won't really compensate for a loaded electrical system. Still better than a 1-wire as those units usually have predetermined limits set, unlike 3-wire units that can compensate.

    And don't disconnect the BAT terminal while the alternator is excited and spinning.
    Electricity will find the path of least resistance.
    With the BAT terminal disconnected, all that juice will find an alternative path, usually back feeding into the alternators diode trio and out the #1 terminal, which is not designed to take any kind of load.
    It only uses the FIELD current for control purposes of the regulator.
    It's why a few posters mentioned adding an additional diode to your system on #1 in sereies. In a factory SI system there is a diode in the excite circuit. But if this harness was not designed/built for an SI type alternator there may be no diode and backfeeding can occur.

    If the alternators you're getting are the same brand from the same shop then I would look elsewhere if they all have the #1 and #2 terminals bridged.

    Also, you can't cut the bridge out between terminal #1 and #2 of a 1-wire regulator and force it to work as a 3-wire alternator. The regulator that is purposely made as a 1-wire is not made at all like a 3 wire regulator. Also the fuse sized resistor inside the alternator is usually removed on a 1-wire, so even if a 3-wire regulator was installed, it still wouldn't function correctly, if at all.
  15. Grandpacharli
    Joined: Feb 17, 2020
    Posts: 27


    Hi Mike , thanks for going into detail about my issue.

    I purchased another 3 wire alternator today and wired it the same as my last I ran for years and still have the same problem. Alternator fires up the ligh goes out and still reading 12v at the bat. If I remove the output lead from the alternator it puts out around 16v as soon as you put it back to power the truck and read the battery it still shows 12.35 v at idle or at any rpm. I will try moving the sence wire to see if that makes a difference ? Maybe then it can monitor the output better. Just strange how it worked before till my last alternator died.


  16. KenC
    Joined: Sep 14, 2006
    Posts: 668


    I would never remove the output wire while an alternator is charging or engine running. Not good practice at all.
  17. I'm at work and haven't had time to read this whole thread from one end to the other. Have you tried swapping in a different battery?
  18. Grandpacharli
    Joined: Feb 17, 2020
    Posts: 27


    Hi , yes new battery and I’ve also recharged the original one still no luck . I’m going to get the new out the box alternator I got yesterday tested today just to see wether it’s burning somthing up instantly as soon as I put it on . I don’t know I’m just lost now I don’t get it.
  19. MAD MIKE
    Joined: Aug 1, 2009
    Posts: 693

    from 94577

    Still redyeing it so I may miss something...
    Battery voltage can be misleading.
    You will want to know what the SYSTEM voltage is doing, if the leads are undersized(too long, too small, etc) then you may be seeing voltage drop at the battery, but the charging side is fine.
    For it to function properly it needs to work as a system.
    Don't do that.
    That will kill the alternator as pointed out above.
    It will backfeed into the diode triples, up the Excite wire all the while cooking the internals of the alternator, killing it.
    What you are seeing is the Alternators Regulator pegging as you have opened the system.
    As far as it 'knows' the battery has been severely drained, 0Volts and infinite resistance. An alternator cannot charge a dead battery and live a long life. It's why there is always the warning to never try to charge a dead battery with an alternator.
    Alternators merely create the float charge. Which is to maintain battery charge and system voltage which can vary between 13-14.4Volts.
    If the battery, fully charged via a battery charger, is not at least 12.6 Volts, its a dying dead battery.
    I'll let as low as 12.4Volts slide for most testing, but that battery may need to be de-sulfated.
    If your battery is only reaching 12.35V fully charged then it is dead/dying, as that is only ~70% charged.

    Have the battery properly fully charged via a battery charger. After being charged allow it to rest. If you can let it rest for ~24hrs that would be best. Check the voltage and verify that it is holding voltage. If it is leaking down then the battery is toast. Verify the battery is clean, any electrolyte or gunk on the battery will self short and slow drain the battery. It needs to be clean and dry.

    (while battery is being charged)
    Verify battery leads and connections are clean and tight.
    Verify wires are not corroded internally.
    Verify all grounds are properly secured and not creating ground loops.
    Negative cable should go directly to the engine block.
    Bonding(negative) jumper(s) should then come off the block and attach to the cab.
    Off the Negative cable battery terminal side there should be a smaller 10AWG going to the body. If the battery is near the radiator support I'll put a grounding stud on the rad support and bond there.
    Connections should all be clean and tight. Use an anti-oxidant compound to promote conductivity.
    Di-electric grease is an insulator, do not use to promote connections.

    The sense wire would better serve you, and your charging system, if it was attached to your main bus. Which is the main junction where power is distributed. On older stock vehicles this is usually the horn relay. If you have a retrofitted harness/newer ASC type fuses, the fuse box may have a main bus bar that is fed from the battery. This would be your best place to attach the sense wire. It needs to see the SYSTEM voltage. Not the alternator. If it only sees the alternator voltage it probably won't change voltage much until there is a higher load/severe discharge(after starting). A sense wire attached to the main system power feed where all the power is diverted from would be best.

    With that said I looked up the American Autowire Classic Update Kit 500560 which is for 1960-1966 Chevy trucks.
    And a note on alternator to be used per the warning sheet;
    Looking at the wire schematic, the harness is designed for a 1'wire' alternator and not for a conventional 3 wire alternator.
    IMO that is just being lazy, why there isn't a dedicated sense wire going to the main bus or the fuse block is just goofy.
    Going back to the Warning Note #3, stock 10SI alternators are not going to cut it. They range from 37-63A. I would use a 12SI, as the smallest amp rated unit was 56A and the largest was 94A.

    One more note;

    It's gives you no usable information, and only damages/kills the alternator.
    26 T Ford RPU likes this.
  20. Grandpacharli
    Joined: Feb 17, 2020
    Posts: 27


    hi Mike thanks for the reply,

    I have stopped do that I watched a YouTube video of a guy doing it . Later found out that’s not a good thing to do but lucky I only done it briefly.

    I took my new and old 3 wire alternator off to be tested and the results show they both still work perfectly! so they are not the problem.

    I will have a play with the wiring this morning as it’s going to be within that no doubt as everything els checks out . I have had a battery on slow charge and it’s reading 12.54v and this is the new one I bought last week for my model a 12v.
    Also took it to a garage yesterday who tried telling me there isn’t an internal regulator which is my issue. So I gave up with him.
    Mike for taking the time to help me out.
    26 T Ford RPU likes this.
  21. Grandpacharli
    Joined: Feb 17, 2020
    Posts: 27


    Still not charging. Still won’t charge with the bat terminal on alternator hooked up to the battery terminal or starter. Idiot light goes out as it should . I’ve gone through most of the cables now looking for one touching chassis but nothing I can see.
    So things I’ve tried:
    1. New alternator
    2. Had my old “failed “ one tested and it’s fine along with the new one
    3. Added an idiot light 12 watt bulb even though I didn’t have one before
    4. Disconnected all the fuses
    5. Disconnected air ride loom
    6. Bought a new battery and had it tested
    7. Hot wired it to bypass the ignition switch
    8. Ran 2 new earths
    9. Ran a new cable from the starter to the fuse panel
    10. Ran pin 2 wire to the main feed on the fuse panel
    11. Disconnected my accesorys
    12. Tried wiring my alternator to separate battery with idiot light to see if it would charge that (no luck )
    13. Checked the positives connections in the back of the starter
    14. Cleaned up my earths
    15. Checked all my lights and they all function as they should.
  22. MAD MIKE
    Joined: Aug 1, 2009
    Posts: 693

    from 94577

    One more quick note on the 'sense' wire.

    Looking at the American Autowire fuse box...

    It appears to be based of a mid80's GM style fuse box.
    Note the single female terminals.
    Those are either constant hot or switched hot.
    With your 'sense' wire, I would plug into the constant hot.
    That way the 'sense' wire will be able to properly monitor system voltage.
    GM used those terminals for additional feeds/wiring after the fact for certain accessories. Which also used a unique terminal that can lock into those terminals.

    Did you let the battery rest after recharging?
    Immediately after charging a battery can have a capacitance that will give a false 'good' voltage reading.
    What was the voltage of the battery before re-installation(disconnected)?
    What is the voltage at the battery and alternator 'BAT' terminal after installation, KEY OFF, ENGINE OFF?
    What is the voltage at the battery and alternator 'BAT' terminal, KEY ON, ENGINE OFF?
    What is the voltage at the battery and alternator 'BAT' terminal, KEY ON, ENGINE RUNNING with accessories OFF?(lights/fan/etc)
    What is the voltage at the battery and alternator 'BAT' terminal, KEY ON, ENGINE RUNNING with accessories ON?(lights/fan/etc)

    Have you done the self test of the alternator per jaracer's post?
    This is how you test an alternator properly without damaging it.
    Note how even though the regulator looks normal it is a '1-wire' regulator. Don't be fooled by how many wires/pins a component has.

    Are there any parasitic draw whit the KEY OFF/ENGINE OFF?(all accessories off)
    Remove the NEGATIVE cable from the battery.
    Attach your voltmeter in series between battery cable and battery terminal.
    Switch voltmeter to 2 Amp setting.
    What is, if any, the ampere draw with all components off?

    Is it though?
    In a well lit garage or outside you may not see if the lamp is dimly glowing, indicating the system is not charging fully. 'GEN/ALT' light bulb should be a regular incandescent, do not use an LED. If LED replace with an incandescent. LEDs are ON/OFF, they will not glow, you need an incandescent here.
    Get a blanket and throw it over your head and dash, start the engine and watch the GEN/ALT lamp. It should go OFF, if you see even the slightest glow then there is something wrong with the charge circuit.

    Does the bracket for the alternator allow for a good ground from the case to the engine block?
    Verify there is a solid ground there(paint/powdercoat/grease act as insulators), or use the rear ground terminal. It is either a 5/16"-18 or M8-1.25 bolt. Verify without stripping threads. Use a strap between alternator and engine block. Verify connections of ground strap are clean and tight. Use an anti-oxidant compound on threads.
    Verified that your dash to column harness is wired correctly per Autowires schematic?
    Verified that all wire connections/terminations(including those made by Autowire) are clean and tight. I've had products where a termination crimped unstripped wire.
    Ignition switch in good order? Just because it's new doesn't mean it's good. Test terminals.
    Is the belt clean and tight? Just because you don't hear it screaming doesn't mean it's not slipping. Glazed pulleys and belts can slip with no audible noise.
    Is the alternator to crank pulley ratio the correct overdrive of 3:1? That rotor needs to spin.
    When the alternator(s) were tested, were they tested with a carbon pile tester? Electronics can test out 'good' with modern light duty 'smart' testers, but they really need to be properly loaded up with a high amp test that only a carbon pile can do.

    I'm still suspect of the alternators charging capability, unless it is an original Delco unit(lots of knock offs around) or rebuilt by a reputable shop or a Delco-Remy rebuild, the regulator may just be cheap '1-wire' unit.
  23. mrspeedyt
    Joined: Sep 26, 2009
    Posts: 729


    on my 52 buick i used a later (78? chevy) internal regulator alternator. heavy 10 gauge wire from #2 terminal to the alternator battery terminal directly and then to +horn relay (and battery+).

    number #1terminal (maybe 18 gauge) into small bulb #57? idiot lite with other wire going to accessory terminal on ignition switch. seemed to work fine for 40 years. i did have a battery cutoff switch (that i usually used) for long term parking. that was between the battery terminal at the starter and then + on horn relay. when i turned off that mid amp rated switch (with engine off) it removed power to everything except the heavy + battery cable to starter. I drove the crap out of that car. B184E99B-9565-4CFA-85B4-DAD4EBD827FF.jpeg
    Last edited: Aug 21, 2021
  24. d2_willys
    Joined: Sep 8, 2007
    Posts: 4,190

    from Kansas

    The sense wire is very important. If it does not go to the battery terminal or something close by, it will not compensate voltage output of the alternator. Make sure that terminal 1 (exciter terminal) goes thru a 57 bulb and on to the ignition switch IGN terminal. Output terminal of alternator directly to battery thru #10 or bigger wire.
    Now for testing:
    With the above wiring do the following:
    1) Remove the battery connection to the fuse block. Then remove fuse block battery connection to the ignition switch. Jumper a wire from battery + post to the battery terminal of ignition switch. (Idea is to remove fuse block from the battery.)
    2) Leave the Ignition switch in OFF position.
    3) Remove ignition wire from fuse block. Jumper from IGN terminal of ignition switch directly to battery + post.
    4) Check voltage @ #2 terminal of the alternator. There should be little or no voltage at that terminal. If there is 12 volts, then the alternator is either a 1 wire or is defective. If no voltage at the terminal go on to step 5
    5) Connect the sense wire directly to the + post of the battery.
    6) Start engine and measure the voltage at the battery. Increase engine speed and verify it now reads above the static voltage of the battery.
    The idea here is to remove all loads except for ignition.With the sense wire going only to the output terminal of the alternator, a heavy load would lower the voltage at the battery, but the sense wire would not do it's job.
    Questions, PM me for more detail.

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