Bigger amp alternator option

Later Model C Bodies - "The Formal Years"

  1. 73 T&C

    73 T&C Senior Member FCBO Gold Member

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    Because I am experiencing low voltage issues when I’m driving at night with the lights, A/C on I’m thinking of going to a 90 amp unit. Horn is weak at these times and, at a traffic light at night, I sometimes get the low amp light on if I’m there for a while.

    Call me lazy.... but I do get why there were two alternators (60 and 90 amp). It’s just that I don’t know what the difference in installation is all about. So.....I have a question of the body FCBO.

    I checked the voltage and it it is at 14 so I’m thinking I’m dealing with an amp issue when all the accessories are going.

    So here’s the question(s):

    Can I make the switch to the 90? What needs to be changed to do this?
     
  2. 78Brougham

    78Brougham Deplorable FCBO Gold Member

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    I believe the bigger alternator came standard with our cars that had the optional electric rear window defogger. Mine has it. Shouldn't be any big deal.
     
  3. 73 T&C

    73 T&C Senior Member FCBO Gold Member

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    Thanks for the quick reply.

    I just don’t want to drop one in and find that I needed to change out some wire or other to a heavier gauge or different plug.
     
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  4. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    You can also run a second lead from the alternator the same size as what ever wiring the car has now. Hook this lead to the hot lug on the starter relay. This will cut the load on the existing wiring from the alternator in half so you don't smoke the existing wiring. You should also run a voltage check on the battery at idle, dim lights etc are usually and indication of low voltage. But you could have corroded connections someplace that have resulted in high resistance and a malfunction of the regulator. Be advised that a bad ground to the effected circuits can also cause these types of problems as well as bad connections in the firewall plug.

    Dave
     
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  5. fury fan

    fury fan Senior Member

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    I put on a 78 (?) amp square-back alt on one of mine.
    Ran a 4ga wire from alt to battery cable (starter relay as Davea said is OK too).
    Be aware that only a portion of your current is now going thru the ammeter, so it will react very little to changes. At least mine does.
    If you are doing this extra current ALL thru the bulkhead and ammeter you may be asking for trouble - those are the weak links.
    My headlights and other non-stock stuff is going thru relays, fed independently of OEM stuff, so not a concern for me. (relay triggers are from OEM side as needed but that's low-load)

    Do some googling on using 90 and 120-amp Denso alternators from the 88-2003 era, they fit a little tight at the battery connection but doable (gonna take a helluva car accident for them to touch). 90 is smaller than the 120 and will fit much better. Look at Rock Auto pics and see which ones come with V-belt pulleys vs serpentine to save a small hassle.

    Also - any modern alt is going to be more efficient and have much better lower-rpm output than a vintage high-power unit. As with cylinder heads, roller cams, etc, this is another area where modern stuff performs better. So a Denso 90 should outperform an older-style 90.
     
  6. commando1

    commando1 Mr. Normal FCBO Gold Member

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    You can run the 73-78 440 OEM style 100A alt. by simply getting its 100A bracket and throw away the idler pulley.
     
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  7. 73 T&C

    73 T&C Senior Member FCBO Gold Member

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    Was waiting for your reply.
     
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  8. commando1

    commando1 Mr. Normal FCBO Gold Member

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    Why can't people JUST answer the f×××××G question??
     
  9. commando1

    commando1 Mr. Normal FCBO Gold Member

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    I gave Jeff a spare OEM 100A alternator (hint hint).
    So many people have tossed the bracket into a junk pile box that they are easy to find.
     
  10. stubs300

    stubs300 Senior Member

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    They're to ignorant to know how, they have to give you the War & Pease version of it!!
     
  11. 78Brougham

    78Brougham Deplorable FCBO Gold Member

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    I thought my answer was quite to the point.
     
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