SHADY280 Posted April 17, 2007 Share Posted April 17, 2007 well ive had the gm 12si alternator swap and maxi fuse upgrade for 2 months now, and the alternator is already screwed. the only gm part on my car spiked at 18 volts, blew the maxi 80 amp fuse!! its not like it was a used alternator either, it was new. could anything on my car cause pre-mature failure to my alternator. im leaving for msa in a week, so it kinda has to make it. after all its only 1400 miles each way. Quote Link to comment Share on other sites More sharing options...
HizAndHerz Posted April 17, 2007 Share Posted April 17, 2007 I would think there would need to be a major load on the alternator output to cause the fuse to blow. Any chance the + battery terminal or cable shorted to ground? Could the back of the Maxi-fuse holder have shorted to ground? I had to put an insulation layer behind the cheap Walmart fuse blocks I used. You might want to check the condition of your harness. Two of my Z's had fried wiring harnesses when I bought them, probably due to the battery not being tied down or the battery being hooked up backwards at some point. I had all sorts or weird problems (car died with healdights or AC compressor on) until I ripped the harness apart and found that the ground and alternator output wires were partially melted. I ended up running new 10gage wires for +12 and ground to the alternator. Is yours a single wire or are you using the F/S plug? Some alternators behave badly if the Sense wire loses connection. BTW, I've got three 280z's with rebuilt 93amp 12si alternators (Duralast Gold from Autozone) and have no trouble with them. I'm a big fan of this swap. Good luck, and let us know if you find anything. Quote Link to comment Share on other sites More sharing options...
SHADY280 Posted April 18, 2007 Author Share Posted April 18, 2007 so i replaced the alternator tonight, no change in the problem. i am using an ebay fuse holder, that has the voltage readout, and a thing to tell what fuses are out. if i disconnect the wire running to the alt main, the problem goes away. ive run #4 ga. to the alternator to the fuse holder, so its all good. plus all connections are soldered. im also wondring if the ebay holder is shorting. im going to try swapping it to a different holder location. i love the swap, just its something causing the full feild condition. i think it also blew the voltage guage. if the blue wire has a problem, where does it run, and what does it control? is it just the idiot light? i need some major help, after all its 1 week to msa, and i dont wanna cancel!!!!! HELP!!! Quote Link to comment Share on other sites More sharing options...
HizAndHerz Posted April 18, 2007 Share Posted April 18, 2007 So, when the alternator's main output is hooked up, what happens? You say the output is 18V? Does the fuse blow each time you hook it up? There are two signals on the 2-pin connector: Field and Sense. Feild serves as a method to "bootstrap" the alternator when the engine is started and is also connected to the warning light. For the alternator to start up, there must be voltage on the Field terminal. That voltage is provided through the warning light snice the other side is connected to the battery through a fuse. If the Field terminal is shorted to ground, the alternator should never turn on and the warning light will be on. The Sense pin provides feedback to the alternator's voltage regulator. If this pin is grounded or disconnected, the voltage regualtor won't be able to do its job and the output voltage may go way up. Check the voltages at the all three of the alternator's connections. You should see between 13 and 14 volts at the main output and the Sense terminal. Also use the ohm meter to check to sure you have a good connection between the alternators ground terminal and the negative battery terminal. Again, good luck. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted April 18, 2007 Share Posted April 18, 2007 I think I may have asked this before, but I know on LS alternators you have to put a resistor in the field circuit HisAndHerz talks about or just what you are seeing will happen. The warning light works a resistor, if it is a bulb. If it is an LED than that is not enough resistance. Wonder if it is the same on your unit. Quote Link to comment Share on other sites More sharing options...
SHADY280 Posted April 18, 2007 Author Share Posted April 18, 2007 when the main line is connected to the alt. stud, everything is fine at idle. when you give it 300 rpm or more, the alternator goes to full field voltage (18v). like when you put a screwdriver in the "D" port. if thats dissconected (the main feed) the whole car acts as if normal, and doesnt blow any fuses. its kinda wierd, everything was fine for some time now, it all worked very well. my volt guage has never been acurate. then i did some voltage drop testing to make sure b4 the trip, and i touched the maxi fuse holder, and it didnt work right after that. the little lights stopped working and the digital readout was acting funny. im wondering if that maxi holder is causing the problem. what else can cause the alternator to go full field??it all seems simple yet very wierd and difficult. Quote Link to comment Share on other sites More sharing options...
SHADY280 Posted April 19, 2007 Author Share Posted April 19, 2007 so its fixed!! (crosses fingers) it turns out my crappy maxi fuse holder from ebay was partly to blame. it was causing some extra draw, 120 total amps!!! thats why the 80 was blowing. my car will draw 100 max. with everything, and i mean everything "on". its mostly because of all the extra eletrical stuff. fuel pump, msd, fans, radio, etc. that and its all old wiring, and old skool components. oh and a slightly dead battery from starting and stopping so often that coupla days. Quote Link to comment Share on other sites More sharing options...
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