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  1. #1

    Default 89 supra comp electrical gremlins...

    My boat seems to have some electrical issues I can't figure out. My alternator is putting out 12.5ish volts checked with a meter. I've roasted a new starter solenoid and melted the negative battery post on a brand new battery Sunday. Last night I replaced.the battery and solenoid and got it cranked. It was still dragging and not turning over easy. How does the battery receive voltage off the alternator to keep it charged? While it was running I removed the negative cable and the motor died instantly. That means theres no voltage returning to the battery correct...??

  2. #2

    Default

    The boat has had electronic ignition added as well

  3. #3
    Join Date
    Sep 2004
    Location
    Hudson, WI
    Posts
    2,651

    Default

    If you melted the negative side of the battery, you have a short some where. Check for continuity between + on the battery and ground. Clean and inspect the cable that goes between your negative terminal and the engine. Check the main cable between your + battery terminal and the starter and the cable between the starter and the alternator. Make sure that the cable from battery to starter is fused. Make sure the cable from starter to alternator hasn't melted against the block and is shorting out.
    Former owner of a 1987 Supra Saltare. Current owner of a Malibu 23LSV.

  4. #4

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    I dont remember there being a wire from the alt to the starter.... Only a ground from the block to - battery terminal, + terminal to starter solenoid. There is a red wire from the wiring harness going to the solenoid.

  5. #5
    Join Date
    Sep 2004
    Location
    Hudson, WI
    Posts
    2,651

    Default

    The red wire going to the starter solenoid is connected to the key and engages the starter when you turn it.

    Do you still have the original alternator? It should be connected to the starter solenoid (or perhaps directly to the battery.) Either way, I'd start by tracing the alternator wires and seeing if they are melted or broken some where.
    Former owner of a 1987 Supra Saltare. Current owner of a Malibu 23LSV.

  6. #6

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    Thanks for the help. Yes the red wire from the switch is connected to the solenoid. I'll unwrap the wireing harness and check for melted wires tonight. Does the altenator chargethe battery through the positive cable coming from the starter solenoid? That's what I can't figure out through eh wiring harness how the battery I's charged...
    Last edited by slickscustoms; 05-15-2013 at 07:20 PM.

  7. #7

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    Does anybody have a good wiring diagram for this boat?

  8. #8
    Join Date
    Aug 2010
    Location
    Feeding Hills, Massachusetts
    Posts
    113

    Default

    If the engine will not run when you disconnect the battery that means your alternator in not supplying enough voltage, that doesn't mean your alternator is bad it means the engines electrical system is not receiving enough voltage, now think about the melted negative terminal, the battery was supplying all or most of the needed voltage, if that neg terminal was at all loose it could have caused this due to arching. I have to assume your alternator has an internal voltage regulator, usually I see 14.5-ish volts coming from the alternator. I am leaning towards a bad alternator, you can have it checked at any parts store. I do not have a electrical diagram.
    There is alot of experience here so keep us updated and you will get the help.

    Fran

  9. #9

    Default Re: 89 supra comp electrical gremlins...

    Quote Originally Posted by slickscustoms View Post
    Does anybody have a good wiring diagram for this boat?
    Does this work? uploadfromtaptalk1368817082943.jpg

    There are a few other ones out there. Try googling "351 wiring diagram"

  10. #10
    Join Date
    May 2012
    Location
    Flowery Branch, GA
    Posts
    83

    Default

    I sent you a copy of the Supra Comp wiring diagram via your email - I hope this helps!!
    kriley
    90 comp ts6m

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