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10 Amp Engine fuse on an 89 FI

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  • F3BZ
    replied
    just FYI if you still want to replace the main relay, or someone else might be interested. even though it says for Mazda, it is the relay used in the festy.

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  • tooldude
    replied
    Question gunner, is this a problem that developed recently, or did the car already have this problem when you got it? The previous owner could have tapped voltage for something, like that radio, at a point where it's going through the engine fuse. If not, I would look first at the fuel pump relay since that is your most recent change. It could be out of spec or even the wrong part. Typical resistance of its type of coil, on Festivas, is about 40-60 ohms & 225 -350 ma. [Relay out & at corresponding (by color) terminals, there should be resistance between BK/R to GN/Y** and BK/W to BK only - If BK/W is connecting to any other terminal, the fuel pump is pulling some of its amps through the Eng Fuse - a short.**The relay contacts are a second **GN/Y that should not have continuity to BK/R with relay unpowered, & no GN/Y to **GN/Y] Apparently you have no schematic and this area is unique to the 1989 EFI. Voltage(+) coming from the Ign switch B/W wire has a splice point where 12V branches to the cooling fan relay, Ign coil & Ign module (also B/W wires), & 10A Engine Fuse. With the Eng fuse removed and Ign Switch on, you can find 12V(+) on the fuse box terminal which is on the Ign Switch side. Ignore that one, nothing on that side can cause increased amps through the Eng Fuse except an over-charging Alternator. Your problem starts at the other fuse terminal. That terminal supplies 12V to the fuel pump relay COIL (from a splice point), main relay COIL, and the alternator regulator circuitry, these all being B/W wires. You need to know which one you're dealing with. That is all that should be in the circuit. To check that entire part of the B/W harness at once for a short, remove Eng fuse, main relay, fuel pump relay, and Alt connector (B/W). Now that harness should be isolated from everything - nothing between ground and any B/W wire (at relay or fuse box connectors). Check with the ohmmeter on Low scale for an infinity or OL reading. With this check, finding a short could be from wiring, or in the fuse box, otherwise a short could be at one of the connectors, or, yes, in the alternator ("new" parts can be defective).

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  • bravekozak
    replied
    Try changing the main relay. The main relay is different than a regular relay. It has a resistor across the solenoid.
    Last edited by bravekozak; 10-11-2014, 08:16 PM.

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  • gunnerw
    replied
    Well the new alternator came in, I installed it threw a new 10a fuse in the engine slot, cranked the engine, it started and ran for about 20 seconds and blew the fuse again. I thought I had this figure out. Any more ideas anyone?

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  • dalebwilson
    replied
    You're most welcome. I hope you are up and running well soon.

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  • gunnerw
    replied
    Yeah, Getting ready to order on from RockAuto now. Thanks for all of your help Dale.

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  • dalebwilson
    replied
    Ok I misunderstood. You will have to get your hands on a good alternator to know for sure.


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  • gunnerw
    replied
    The problem is that right now if am to drive it I will have to leave the alternator disconnected or I will continue to blow the 10a engine fuse.

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  • dalebwilson
    replied
    Your fusible links could have been loose, weak or corroded causing issues. Try running and driving it for a while with the PAL fuses installed.

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  • gunnerw
    replied
    Ok I have disconnected all three wires leading to the alternator. I have then reconnect each wire alone to the alternator. With each wire the car crank and runs. I also removed the Head Fusible link (which I replaced all fusible links with large box fuses as pictured) as the car was running and it had no affect the car kept running.

    I am wondering at this point if the alternator is the problem. When the 10a fuse does blows its never instant its always a slow bloeimage.jpg

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  • tooldude
    replied
    Like dalebwilson is saying ^. I don't have a specification for Festiva, but a typical alternator of its type should not have more than 0.5V AC ripple. Yours is more than double that and rises extremely fast from near 0 (it is there) to 8.1% of the DC. Regulated voltage is over the FM spec of 14.4V to 15V and the alternator being in-circuit blows the engine fuse. It sure seems like an internal problem with the alternator. There is no direct short to ground or the fuse would blow instantly. There is resistance in the circuit and the fuse is blowing relatively slowly because either there is an over-voltage or a resistance has been altered (lowered).

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  • dalebwilson
    replied
    Try pulling the HEAD fusible link and see if the engine stays running.


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  • dalebwilson
    replied
    Yes. You definitely have a direct short circuit coming off your alternator that is blowing your engine fuse. You may have found your problem.


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  • gunnerw
    replied
    Funny say headlight because the left headlight is burnt on the inside

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  • dalebwilson
    replied
    I would do that to help you narrow down the short circuit. One circuit is the headlight and the other is the meter circuit with the charge lamp in the instrument panel.


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