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Discussion Starter · #1 ·
I have a 1995 Defender 110 (RHD) with 300tdi and I swapped the original 65A alternator for a 100A disco alternator about two months ago. There were no issues until one morning while warming the truck up for work, I noticed the B+ wire had come loose on the alternator while it was running. I was in a hurry and, instead of turning the vehicle off and disconnecting the battery, I just reconnected the wire without thinking. The alternator sparked and the vehicle went dead and there was no longer a click or anything when I turned the key in the ignition. I disconnected the battery and got a ride to work.
After work, I checked connections of all the wires to the starter and alternator. Before connecting the battery cables, I checked their condition with no issues and confirmed the negative ground to the transfer case was clean as well. Everything seemed fine so I reconnected the battery cables, and without even turning the ignition, the engine bay started billowing thick white smoke. After spraying it down, I saw the following damage.

ALTERNATOR
462159


STARTER (I disconnected the cables before the picture was taken). The black wire at the bottom of the picture goes to the engine bay fuse box and I had it connected to the starter.
462160


It's probably something really obvious but I hope someone can help me figure out the problem. I have searched this forum and other defender sites with no luck.
 

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Where does that black wire go to exactly?


You shorted the battery That's why everything caught smoke and almost went up.

You're obviously going to need an entirely new engine harness. So you might as well take the engine harness off of the motor and check it.

Also check and make sure that the battery positive to starter is not shorted somewhere either.
 

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Discussion Starter · #3 ·
I'll have to check the fuse box for the exact routing of the black cable.
I removed the battery positive to starter cable and it looks brand new so could it be an issue with the negative cable? The engine harness was also new...recently received from autosparks and I took this picture before connecting it. #1 was connected to the same wire as the old harness but I still don't know its function. #2 was not connected to anything on the old harness so I zip tied the two plugs to the transfer case. #3 was connected properly but I don't know the function.
462161
 

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similar to water, current flows the path of least resistance. something grounded and that is where followed and your cable bq. first identify reason of failure, could have been lack of ground, could have been a chaffed power wire, or internal alternator failure, I have seen alternators catch on fire due to internal failure.
beyond that your only option is a new harness.
 

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Discussion Starter · #5 ·
Since the harness was literally brand new and recently installed and the positive battery cable has no fraying and looks new, it must be the ground cable so I will remove it for inspection as well...lots of grease on that one.
I have already removed the alternator and will disassemble it to see if there are noticeable issues with the rectifier, regulator, or diodes. Do I need to increase the gauge of any wires due to increasing from a 65A to 100A alternator?
 

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I really doubt it's the ground cable. Somewhere that is battery hot shorted against the engine or body of the truck. Since it's melted all the way up to the alternator there is a chance that the alternator died internally and shorted internally.


The steps I would take would be as follows:



Remove alternator and take to any auto parts store for testing

Remove and replace engine harness

Remove and inspect all positive battery cables that connect from the starter lug to the battery. Including that rogue black one that you have for some weird reason.

Remove and clean connection points of the battery to chassis and engine to chassis ground cables then replace.




The good news is that you caught it and it didn't engulf the truck.
 
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