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Thread: Weird battery light activity in 95 SC Auto... Help!!

  1. #1
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    Aug 2002
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    Weird battery light activity in 95 SC Auto... Help!!

    So I was on my way home from work today and looked down to see the check gauge light was on (I was getting towards the 'E' on the fuel gauge. The low fuel light was on as well, so I thought this was normal. Several miles later, I look down and the check gauge light is now out, but the battery light was on! The car was running fine, no apparent problems noted. Towards the end of my 50 mile drive home, I was looking down and hit a bump, the light went out for a split second, then came back on. Still no problems with how it runs.

    I stopped for gas on the way home, full tank, and get back in the car and the battery light is out. When I check the voltage at home, the idle voltage is 13.66-13.7, not changing at all when revving the engine. I have new terminals on the battery, the car starts and runs fine.

    Any thoughts?

    Thanks All!

  2. #2
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    AFAIK, in a typical fail, the light on means you're running off the battery. Might want to have the alternator checked.

    If the battery was low/dead, and the new terminals meant some sort of battery related maintenance, keep in mind the alternator should not be used to charge a depleted battery...that process can overheat the rectifiers/diodes in the alternator, killing it in the process.

    Light on/off tho, hitting a bump...seems odd, of course, especially if idle volts are up. What is the battery voltage, key off, headlights on? At least 11.3? Steady, or drops? Fluid in the battery up where it should be? Did the cables look clean/not green when you hung new terminals on them? What was up that they were needed?
    Last edited by KMT; 03-14-2019 at 08:44 PM.

  3. #3
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    I just checked and checking the battery voltage with nothing on at all, it is 12.67 volts. With the headlights on, it goes down to about 12.44V. It cranks up every time, no problems. The battery is fine, didn't need any charging when I got it, however, the terminals were in sad shape. I replaced terminals and cleaned any corrosion off the primary wires.

    I still need to check / clean the cable at the starter and wherever there are any chassis grounds.

    I just thought it was weird that it came on, the batt light, when I was really low on fuel, and then went off when I filled it up.

  4. #4
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    Well then...given the age of these cars, it wouldn't surprise me of there was some sort of backfeeding between those warning light circuits. I'd have to study the EVTM to know if that's likely, tho.

    I'd keep a AAA card in my wallet and see what happens next

  5. #5
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    Quote Originally Posted by KMT View Post
    I'd keep a AAA card in my wallet and see what happens next
    Bingo! At this point with a 30 year old vehicle, thats a good idea.

    As for the light on/off issue.. it could be a connection somewhere that got jostled, but more likely the alternator is on its way out. Best thing is to test the running voltage; it should be 14V or higher.. If the light comes on again, check the running voltage again. If its 12 or less, then the alt is not charging. Take it out and have it tested. As for a replacement, you're better off with a known working OEM used one here as the components were better quality. Remans have a bad track record. Some are DOA, others will fail in 6 months or less. It can take 3 tries to get a good one and that means you might find yourself stranded.

  6. #6
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    Light is back!!

    So I don't think it is related to the fuel low light. I drove to work this morning and it came on as soon as I started it! Arghh! I did notice that when I revved the engine above around 2500rpm or so, it would go out. Or, if I was above 2100rpm-ish on the highway it would go out. I can sit there and watch it as I approach 2100rpm. It will start to flicker and then as soon as I hit that certain RPM, it goes out.

    Yet, it still runs great! I am thinking maybe the voltage regulator on the alternator is going out. I doubt it is the original, have 172k miles on it (well, more than that as my odometer gear needs to be replaced as it isn't working).

    Question is, if it is the alternator, knowing that the local parts stores sell mostly junk, I wonder if I should take it to a shop and get it rebuild / upgraded?

    Thoughts?

    Thanks Everyone.

  7. #7
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    Local shops use the same internals as the parts store vendors. Shop warranty.

    As for junk...I think some of that bad rep is from people not charging the battery on a charger first.

    Don't forget you can see if someone here has a used one they'd sell, but the freight might not be trivial. I'm sitting on three spares, but I've only had to replace a failed unit once in ten years of ownership w/110k on the car.

  8. #8
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    The alt in my Black car just went south. I had a spare (of course!) and all is well. One thing I noticed after removing it, was the main terminal had a lot of oxidation+rust. It is possible that this is/was the issue. I cleaned it up, and I'll take it in and have it tested. What comes to mind tho, was 3 months back I left the lights on and the batt was completely drained. I got a jump start and drove it off (you don't have a choice in that situation) for about 15-20 minutes. When I got it home, I put it on the charger since I know all to well what that does. The normal rubber boot for the stud, was long gone.. crumbled to dust which leaves the main stud exposed to the air. That, combined with the elevated heat, is likely what caused the corrosion.

    Something else to look for.

  9. #9
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    Quote Originally Posted by TbirdSCFan View Post
    Something else to look for.
    👍 ........

  10. #10
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    Quote Originally Posted by phils89sc View Post
    Question is, if it is the alternator, knowing that the local parts stores sell mostly junk, I wonder if I should take it to a shop and get it rebuild / upgraded?

    Thoughts?

    Thanks Everyone.
    I'd get it rebuilt, or get an upgraded new one.

    Then again, the local guy is rather choosy in what parts he uses, and his Dad used to do the alternators and starters for me back in the 70's.

    I've done a warranty claim with them once in 40+ years ...

    RwP

  11. #11
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    Well, I brought my SC to my local Orielly's on the way home from work. They tested the alternator and it said it was bad. I guess it was putting out only 11.7 volts. So I guess I am in the market for a replacement. I have a local U-Pull-It that I can go to tomorrow, and have heard stories of the 3.8L Mustang (later new-edge style) having an alternator that will work, but heard that there may be some issues with the SC 8-rib pulley not working on it, sticking out too far or something). Can anyone give me suggestions on what to look for? I would like at least the same amps capability and can make minor mods for fitment.

    Any ideas?

  12. #12
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    I'd go to TBSCshop and get one of those used ones. In fact, I was about to do that same thing, but turns out my Alt was not bad, but rather the oxidation on the terminal was the problem. I had a spare, which I installed and am now using, so it looks like I now have a new spare.

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