Blew the 80 AMP main fuse tonight. *** STILL BROKEN *** - Page 3 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 09-03-2011, 06:18 PM   #41
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Well **** me. Good thing my WHOLE HARNESS BUILD IS BASED OF THE MITCHELL DIAGRAMS..



Although I AM using a bit of common sense, and the old harness as a reference.
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Old 09-03-2011, 06:47 PM   #42
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Quote:
Originally Posted by FRT_Fun View Post
Well **** me. Good thing my WHOLE HARNESS BUILD IS BASED OF THE MITCHELL DIAGRAMS..
It's ok. On average, the Mitchell diagrams typically only have 3 or 4 critical mistakes per page.
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Old 09-07-2011, 09:10 AM   #43
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Finally got some days off work and pulled the alternator last night. Ran it up to Advance Auto and they put it on the machine. Guess what - the rectifier tested good. I've never been more disappointed that I had something not broken. Not sure where to go from here. It just HAS to be the rectifier. I don't get it.
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Old 09-07-2011, 09:34 AM   #44
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What if you switch on without the alternator in place?
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Old 09-07-2011, 09:38 AM   #45
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Hmmm, had not done that but would be interesting to see what would happen.
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Old 09-07-2011, 10:32 AM   #46
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What happened:
- car dies, 80a blows (wire is laying on the exhaust)
- put in another 80a and it blows instantly
- tow car home and fix wire
- test across open fuse and see 12V
- test across wife's MSM open fuse and see 0V
- pull wire from alt and see 0V
- determine that my alt is bad (bad rectifier probably)
- get alt tested and find out all is fine with it
- scratch head and rethink

I have never blown a fuse after the wire was fixed (haven't tried). I just put the fuse in, pulled the NEG battery cable and measured for amps across battery cable and NEG battery post (reads 0.1 amps - dark current). This seems fine but the alternator is still out. I'm wondering if I have 12V but only 0.0000000001 amps. Could it be that I was just inventing a second problem (blown alternator)? I'm going to have to put the alt back in and see if the fuse blows. I hate doing it (I don't have another fuse - 3 was my limit). I'm hungry and tired (night shift) so I think I am going to grab a bite and take a nap.
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Old 09-07-2011, 02:15 PM   #47
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First off, stop trying to measure voltage across the fuse. The only thing that's going to tell you is whether the fuse is blown or not. If it's blown, you will see 12v across it. If it's not blown, you will see 0v across it, regardless of how much current is flowing through it.

Try hooking everything up (except the alternator) and start the car. If it runs and does not blow the fuse, then attach the alternator. If that blows the fuse, then the alternator is bad- end of story.
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Old 09-07-2011, 02:55 PM   #48
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I still don't understand what you mean by testing voltage across the fuse, do you mean you are putting one lead on the incoming side of the fuse and the other on the outgoing side (one on battery side and one on load side)? I agree with Joe, that's not a good way to test for your problem.

As much as I hate to say it, Joe's suggestion above probably should have been one of your first steps. Let us know what happens though.
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Old 09-10-2011, 05:42 AM   #49
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OK, the car is fixed and back on the road. There was nothing wrong with the alternator after all. I did take it to three places to get it tested (they were across the road from each other). Two said it was fine and one place said the rectifier was bad. I've since learned (well, learned before and that was the reason I wanted to see what three different places said) that those testers are not to be trusted. Anyway, I was seeing 12V across the fuse socket (with the fuse removed). No, that 12V was not supposed to be there and did not exist on my other Miata. What I did not think to test for until I was told the alternator was good was AMPS. I was getting 12V but only 0.03 amps (what I thought in post #46).

In hind sight, testing for amps should have been my first test. Believe it or not, that is the first time in my life I have ever switched my meter to amps (never had a reason until now). So, in the end I learned something and fixed a problem (hanging wires) on the car.
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Old 09-21-2011, 11:23 AM   #50
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rmcelwee, i just experienced the same thing after getting the car for 3 days. my 80 amp fues blew and i had the car towed to my shop. I had a suspicion that the PO had jumped the car a few times and that may have weakened the 80amp fuse over time. My mechanic says that fuses go from time to time and made the same comment as you, you're luck it blew locally and not happen while you were a hundred miles away.

Glad to see your car is up and running again. g/l on the car sale.
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Old 09-21-2011, 12:15 PM   #51
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I've never had a fuse "just go". Nope, "millions" of miles under my belt and have not seen it. I guess anything is possible though.

Did it happen to you a hundred miles away? I had TWO spark plugs back out of my pickup truck about 300 miles from home once. Like I said, anything is possible.
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