Keeps Blowing Alternator Fuses

[Livid]

My alternator fuse blew about a month ago. I knew my alternator was bad so I replaced it thinking it had a dead short. After replacing it I put in a new 120a alternator fuse and hooked my battery back up. As I was putting the positive terminal on it arced and immediately fried the alternator fuse once again. There has to be a dead short somewhere right? I just had a SFMU installed. Is it possible that something is unhooked around the fuel rail where the SMFU fuel line would be tapped in? Or is there something else that is common, that I could check for, such as a bad starter? Are there any tests I could do to narrow down my problem? Thanks for any help.

Also, before I replaced the alternator, if I leave the fuse out, the battery measures 12v. When I hooked up a battery charger to it and replaced the alternator fuse the battery voltage would bounce back and forth every few seconds.

 

[Old Mitsu Tech]

So, when you put in a new fuse and hook up your battery it arcs and blows the fuse?

Unhook your alternator and try it. If it doesn't arc and blow the fuse it's likely the alternator. If it still does it, get a circuit breaker and hook it between your battery and battery cable. Take a test light and start looking. When the light is flickering you are on the hot side. When you move down the wire and suddenly it quits blinking you have moved past the short. Just back up and you should find it. You can also use a compass needle for this as the circuit breaker opening and closing makes a magnetic flux and likewise when the needle quits moving as you move it down a wire you have gone past the short.

Good Luck

 

[power=dsm]

You can also use a compass needle for this as the circuit breaker opening and closing makes a magnetic flux and likewise when the needle quits moving as you move it down a wire you have gone past the short.

Good Luck[/QUOTE]

using a compass for finding a short?? Never thought of that before thk!

 

[Livid]

I can't even put a fuse in or it would blow it, so how do I keep currect flowing long enough to test it? I used a voltmeter to test the starter and some other things and everything was at 11v . This is probably because the battery isn't fully charged, but this shows me that the problem is on the alternator side of the fuse. Does the line on the alternator side of the fuse just go to the alternator? Are there other things I need to check on that side of the fuse? Should I start by replacing the Alternator --> Battery cable? The alternator was just rebuilt so it is very unlikely that the alternator itself is the problem.

 

[Livid]

Ok, I tried a few more things. Even if I completely disconnect both terminals from the alternator the fuse still blows. I'm not exactly sure which side of the fuse is shorting out though. I don't know if it is the line going to the alternator or the line coming from the battery. If anybody has any more tips for checking please let me know. The curcuit breaker will cost $55 just for a 50a breaker so I'm just stocking up on 80a fuses for testing.

 

[Old Mitsu Tech]

No, use a 10 amp circuit breaker. You are only trying to find a short. It doesn't need a million amps to find it. It just needs to trip to help find the short.

Good Luck

 

[Livid]

Problem Solved, thanks for all of your help.


Turns out it was the cable going from the fuse towards the alternator. Tracing the cable about 2 feet past the fuse where it starts to wind down below the intake manifold it was melted and wires were exposed, it must have touched the block to cause a short. I'm not exactly sure how it melted the wires, but I rerouted the wires so this wouldnt happen again.

 

[Old Mitsu Tech]

There you go. Good Job

 

[Drifter27_04]

Can anyone tell me the part number for the alternator fuse at the mitshi dealer?