'88 Testarossa Battery light off at idle yet illuminates above 3k rpm | FerrariChat

'88 Testarossa Battery light off at idle yet illuminates above 3k rpm

Discussion in 'Boxers/TR/M' started by NashGTS, Aug 26, 2024.

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  1. NashGTS

    NashGTS Rookie
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    Aug 4, 2019
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    Bryan phillips
    Hello, I have an odd situation with my '88 testarossa. The battery light is off at idle yet starts to illuminate as rpm's climb. At 4k it's fully illuminated. The alternator was rebuilt not long ago by a good shop in the area. I've cleaned all the contacts in main harness in the engine bay feeding the alternator. I measure 14+ volts at the battery when the engine is running and I can drive at night with the lights on for extended periods without issue so I'm sure the battery is getting charged. I have replaced the dash lights with LED's but years before this issue appeared. Moreover, this doesn't always happen. It seems to be an issue one week, and then it will go away in time and then come back again. It's annoying when it does happen, so I'd like to find the root cause but presently, I'm at a loss. Any help would be much appreciated.
     
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  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
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    Did you measure the battery (alternator) voltage when that warning light was wrongly illuminated? That warning light is really only meant to detect a broken alternator belt. It will often wrongly illuminate when something inside the alternator goes haywire, but that is not its intended function.
     
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  3. ferralc

    ferralc Formula 3
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    #3 ferralc, Aug 27, 2024
    Last edited: Aug 27, 2024
    I’ve had two alternators failing on me with the same symptoms, one time I was left stranded on the highway when the battery ran out and the second time I was actually coming from the shop to see why the light was flickering, they tested the alternator and it was working “fine”, just to had actually smoke coming out of the alternator on my way home and I was able to make it back to the shop with the battery almost dead.
    Before the second one failed I did several tests, like measuring the voltage with a radar detector plugged to my cigarette lighter while driving and I got good voltage.
    For me if I see that light again I know my alternator is about to die and I wouldn’t risk it, even if I get good voltage.
    Somehow my car likes to eat alternators so the mechanic told me back then that the only permanent solution was to upgrade the alternator to the one in a F430 if I recall correctly (AC Delco vs Denso???)
    These are the videos I took days before the alternator suddenly died with smoke and everything.







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  4. NashGTS

    NashGTS Rookie
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    Thanks so much for the responses. My alternator is the Delco variety and I had it rebuilt due to age only, prior to any issue. I think tonight, I'm going to take a drive with my DMM on the battery leads and see what I get for max, min and avg. Another piece of info I find interesting is that the battery light is on when I start the car and goes out once I rev the engine a bit. This I've always associated with the need to "charge" the diodes upon start. Then once I drive away the light can start to illuminate one the rev's exceed 2k. This later issue seems to come and go - month to month. more to come - thanks again....
     
  5. NashGTS

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    Well, I'm going to have to wait for the problem to return. I set up my DMM on the battery to monitor voltage while driving and no light issues upon start up. All worked as it should. Problems don't take care of themselves, so I'll have to wait for it's return to get more data ........
     
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  6. ferralc

    ferralc Formula 3
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    Sep 2, 2010
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    When I did that I ended up stranded on the side of the highway.
    I would go back to the shop that rebuilt the alternator and tell them something is off. As Steve said if the light is on is because something inside the alternator has gone haywire.
    And also the blip to get the light off at cold start is not normal either, do a test, start the car and don’t blip it and measure the voltage with the light on, I would guess the voltage is not right until you do the blip.
    Good luck


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  7. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
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    The light at start up which goes off when you rev it the first time is a form of test, to prove the alternator light and its associated circuitry works. Normal.

    Does the voltage drop above 3k rpm?
     
  8. ferralc

    ferralc Formula 3
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    I know it is common and some cars here do that (battery light until you blip it) but in my experience in a perfectly working alternator there should not be any light at cold start than needs blipping the throttle to make it go away.
    Of the 3 alternators I’ve had, the one that lasted the least was the one that was doing that, after it was rebuilt there is no need to blip the throttle to make it go away, it goes off automatically without any throttle input.
    Actually when that happened there’s a very particular noise you don’t hear until you blip the throttle that makes me believe the alternator is not really working until you blip it.
    Basically I don’t think there should be a throttle blip by default to make the light go away or (if my theory is correct) to make the alternator start working.






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  9. turbo-joe

    turbo-joe F1 Veteran

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    this alternator bulb gets plus ( + ) by the ignition key when switch to "ON" and minus ( - ) by the alternator when engine is not running. as soon as the engine runs the alternator brings plus ( + ) and the bulb turns off because getting plus from both sides. so may be the alternator brings much more voltage than those normal 14,4 V then the bulb also will go on. or you have problem with the plus ( + ) from the ignition switch?
     
  10. theunissenguido

    theunissenguido F1 Rookie
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    Jan 21, 2004
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    I have this situation for several years on my mondial QV. The alternator was tested twice and did not show any problem. So I live with it because I never drive at night with that car.
     
  11. NashGTS

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    My issue with the battery light requiring a blip of the throttle to go out upon start was present before and after I had the alternator rebuilt. I thought a rebuild would take care of this and it did not. The voltage at the battery is steady through the rev range, however it shows only a little over 12V, until I blip the throttle and then it jumps over 14V so the light is telling the truth. I need to monitor this voltage while driving, once the problem returns. The alternator shop has been around a long time so I'd like to think they knew what they were doing. This weekend is another opportunity....
     
  12. ago car nut

    ago car nut F1 Veteran
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    I have that slow Alt. on other European cars. I believe the execitor in the Alt. needs a voltage boost at 1st.
     
  13. ferralc

    ferralc Formula 3
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    #13 ferralc, Aug 29, 2024
    Last edited: Aug 29, 2024
    Exactly my point
    That is NOT a normal behavior, the alternator doesn’t really start working until you blip it, the belt IS turning but not enough to make it start, you can actually hear it working when you do the blip, it is a very particular sound. When that happened to me, the alternator eventually did the same as yours with the blinking light, just to suddenly go out with smoke and everything.
    Not saying the shop doesn’t know what they are doing but if I were you I will look for a new alternator to fix this issue once and for all.


    I actually found the videos in the conversation with the mechanic
    This is a video he sent me telling me “everything is fine come get your car”

    https://youtube.com/shorts/_024j02PRIo?si=TceJhdFpl2k5cQKK

    2 miles away I saw smoke coming out of the back of the car and I barely made it back to the shop with an almost dead battery

    https://youtube.com/shorts/3x8KhhZjM7E?si=h08iV-NSxLsQFZFI



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  14. ferralc

    ferralc Formula 3
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    Yes it is a commonly accepted feature with older European cars that the alternator doesn’t get excited until it reaches certain rpms threshold but I don’t think it is a normal behavior with the TR alternator, I believe the alternator should start working right away without any throttle blip, I have no idea what would be the issue (voltage regulator, bad brushes??) but an electrician expert like Steve M could say if that’s normal or not.



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  15. versamil

    versamil Formula 3
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    Every post here is a gold mine of information. So I have a 1987 328GTB that the alternator light stays on until you rev the engine. You can be driving down the road and the light will NOT go out until you rev the engine. Obviously is NOT charging until the engine is revved. I KNOW the idiosyncrasy and have lived with it for 10 years. Never been a problem until I let a friend drive the car and forgot to tell him above revving the engine. Whoops.

    Pretty sure it's an original alternator as the car only has 15K on the odometer. It IS a Bosch alternator.
     
  16. theunissenguido

    theunissenguido F1 Rookie
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    My 328GTS 1987 does the same thing. Already asked Steve if he knows what the problem could be but even he does not know. I just live with it ....
     
  17. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    I'd say that it's not a super-uncommon behavior but also not a common behavior. Never had that symptom on my ex-F alternators -- the warning light always went "off" at engine start-up. If the RPM required to "activate" the alternator was low enough that would always be exceeded just in normal cold-running use (like say 1500-2000 RPM), I wouldn't worry about it. If it required a high RPM, like 3000-4000 RPM, that would be worth trying to fix IMO.
     
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  18. moysiuan

    moysiuan F1 Rookie
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    I wonder if people experiencing this have AGM batteries, that require a higher charging voltage than these alternators are designed for?
     
  19. ferralc

    ferralc Formula 3
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    Standard battery in my case



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  20. ago car nut

    ago car nut F1 Veteran
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    Optima type batteries. If the battery is dead below 10.5 vdc, Don't charge with alternator or old type battery chargers. You need a lead acid battery between. Ask me how I know? I burned up an alternator on my hot rod after jump start dead battery. The newer battery chargers are designed to charge newer type of batteries.
     
  21. ferralc

    ferralc Formula 3
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    This is a cold start of my car
    Rpms barely reaching 1k and the light went off automatically
    I think a lazy alternator that requires a blip of the throttle to be excited (while accepted as normal-ish behavior) is an indication that an alternator is not working perfectly. My 02 cents

    https://youtube.com/shorts/VYuFpc2qLT0?si=rPNHl2GfWAzJOuaC




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