Hi all, so i am having an issue with my 1995 T4R 3.0 V6 where i am blowing the 80A ALT fuse. So i was having an issue where it was idling low and so i changed the spark plugs, wires, cap & rotor and adjusted the throttle control valve to get it idling around 800 and it was running great. I had it parked for a couple days after, i did that work to and then i fired it up to move it a few days later, i put it into gear, turned the corner and then lost all power (fuse blew). I have since replaced the once and as soon as i reconnected the battery it blew again, so I then disconnected the alternator, replaced the fuse again, vehicle fired right up, i shut it off and then the fuse blew again after i shut the vehicle off with the alternator disconnected. Sorry for the long writeup, i just want to get all the information out here. Im pretty confused as i figured once the vehicle fired up with the alterntor disconnected i was in the clear to start looking for a bad alternator ground. Does anyone have any ideas? Thanks in advance.

 

Only the 80-amp fuse and nothing else blew? It takes a lot of power to blow that. Most likely something upstream of the smaller fuses but downstream of the 80-amp fuse is shorting to ground.
Look at schematic and see what circuits get power between small fuses (40-amps?) and 80-amp Fuse. Inspect those for short to ground.
I do not have schematic for 3.0 handy, but I would thoroughly inspect the entire length of the "B" (alt to batt) wire for worn out insulation short to ground

 

Yes just the 80 amp. Could it still be something downstream of the 80 amp fuse if its only the 80 amp that is blowing? i gave things a look over and as best i could tell there was nothing out of the ordinary.

 

Immediately downstream of 80-amp fuse but upstream of any other fuses, or else the lower rated fuse.wud blow first.
Need schematic, and see what fuses / fusible link look like, to narrow down.

 

just had the mechanic friend over and we spent 2 hours testing and looking for a bad wire or any sign of an obvious short circuit to no avail. we had continuity between the positive and negative battery leads so it could really be anywhere. I guess the next step would be to get a wiring diagram and start unplugging things?

 

This is from the 93 FSM, showing all circuits downstream of the 80A fuse:

 

Yes, but what continuity? How many ohms? Dead short?
From Paul's schematic below, inspect wire to heater relay pin 5, Taillight control relay pin2, wire to stoplight fuse.
Power line to headlight relay, not shown but most likely connected directly to 80A fuse

Paurl,
What goes below the AM2/30A fuse? Battery?

 

Here's where Paul22RE got the diagram. http://web.archive.org/web/201204170.../2powersou.pdf
I'm sure he wasn't concerned about what was "below" the AM2 fuse, because all of that is on the battery side of the 80A fuse.

Unplugging the heater relay and the taillight control relay could help, but each of those circuits have fuses downstream, so I'm pretty sure this is just an issue where a wire on the way to these relays or fuses is shorted to the frame.

 

Here is the rest of that diagram from https://web.archive.org/web/20120417.../2powersou.pdf

 

This video might give you some ideas. If nothing else, you should build a "high current test light" like he shows so you can search for the problem without going through a whole box of $5 fuses.

 

So i went out to start doing more tests and and things you guys suggested but just for fun i tried disconnecting the alternator and hooking the battery back up and lone behold i didnt blow the fuse and i put the key in and the dash lit up. I connected the connector on back of the alternator and then put the battery back on, still good, then i hooked the black wire onto the stud connected to the alternator and connected the battery and got smoke coming off. i traced that wire back right to the fuse box and everything looked really good, there is a bit of corrosion right on the lead of the wire where it connects to the alternator stud but other than that it looks normal. Is there a chance the alternator is fried? =Would it be worth it to replace the alternator and see what happens or do you guys think its definitely a wiring issue? Like i said earlier i changed the spark plugs and wires recently and i was rooting around above the alternator doing those, i could have bumped something or gotten dirt into the alternator or whatever. All the advice is really appreciated.

 

Yup, that's why it's called the "ALT" fuse. A dead short in the alternator (often in the diodes) will blow the 80amp fuse.

I don't know where you are, but if in the U.S. just about any auto parts store is happy to test your alternator for you -- you don't have to spend $100 on an alternator just on a guess. They'll test it for free because they hope to sell you a new one, so check out RockAuto (or your favorite source) first so you'll know if the parts store replacement is a good-enough deal or terrible.

 

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From "stud" I'm assuming the black wire is the "B" Alt-tobatt wire, so Like Scope says^^^.
Also if you have a multi-meter, with everything disconnected from alternator, measure resistance of that stud to ground. Should be LOTS of Meg-Ohms ( I don't remember what I read on mine). If only a few ohms or less defective alternator,

 

Not sure if this helps any, it is from a 1995 Electrical Wiring Diagram supplement (EWD216U)

 

I'm having a hard time finding black "B" wire on above schematics, but most likely cause of ONLY 80-amp fuse/fusible link blowing without smaller fuses blowing is short from "B" wire, through alternator, to ground. Multimeter can verify that.

 

I don't see a black wire on these. This is the charging circuit page.

I do recall realizing while doing my 5vz harness, that this book, the '94 factory manual - overall diagram, and reality did not always match 100%.
But the 95 has always matched this supplement (two posts up) each time (IIRC!!) Don't recall 'xactly tho.

ps. I'll come back and erase this as soon as you're done borrowing it, so there's no issues involved.

 

Yeah, O.P.'s post made me wonder, too . Typically "B" wire that connects to alternator stud (output) terminal is thick and white wire.

 

Hey all, thanks for your help, turns out it was something shorting out inside the alternator. I swapped the alternator out and now its running great.

 

Cool. that's what we thought.
Pls confirm, is your B wire really black on that model?

 

Yup B wire is black.