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PostPosted: Wed May 27, 2015 9:16 pm 
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Location: Ottawa, Ontario
So I was cruising around last week when I heard a "pop" and started losing electrical power. Limped it home where it finally died in the driveway. Looking under the hood I found the Alternator 100 amp fuse was blown. I started investigating and found the alternator to be fine along with the + wiring going to the alternator.

This is where it gets strange... The fuse next to the alternator fuse labelled "fuse B+" is grounding out, completely solid short to ground, but this fuse is NOT blown. It seems to be on the same circuit as the alternator fuse though. Does anyone know where these "fuse b+" wires go? Their going into the cabin but I loose them there, one white/red stripe, the other is black/ red stripe. I have no idea where to go with this next and the frustration is building!

Any help is appreciated!


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PostPosted: Wed May 27, 2015 10:01 pm 
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Not sure if you have been this way yet, but it is worth a try:

FSM 89 turbo electrical manual

I would go out to the car but it's dark and the light is on the other end of my garage from the way the car is parked (JSB'ing at the mo).

I can have a look tomorrow if needed.


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PostPosted: Thu May 28, 2015 11:29 am 
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Thanks! I finally found all the factory manuals Chad left me with the car. Looks like it ties in with the starter and ignition... Do you happen to know where the relay is for the alternator? For the ignition switch, will that mean removing the dash?


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PostPosted: Thu May 28, 2015 12:27 pm 
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Alternator to fuse block = twisted pair of 10 or 12 AWD white colored wires. Fused at underhood fuse block.
Starter is direct to battery, no fuse IIRC. Starter grounds through block and back to the frame just below the original battery location RF. Frame rail has a tapped hole for a 12mm headed bolt, pointing straight up just ahead of the trans mount area.

What circuit is staying live that shouldn't be?


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PostPosted: Thu May 28, 2015 2:21 pm 
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Quote:
Alternator to fuse block = twisted pair of 10 or 12 AWD white colored wires. Fused at underhood fuse block.
Starter is direct to battery, no fuse IIRC. Starter grounds through block and back to the frame just below the original battery location RF. Frame rail has a tapped hole for a 12mm headed bolt, pointing straight up just ahead of the trans mount area.

What circuit is staying live that shouldn't be?
One of the circuits is grounding out. If you look at the under hood fuse panel, right beside the Alternator fuse is a fuse labelled "fuse b+". This fuse seems to be on the same circuit as the "alternator" fuse, at least it is for me... When I use my meter, I see a solid ground on the alternator twisted 10GA wire, when I remove the "fuse b+" fuse, the ground is gone. I have no idea where these "fuse b+" wires go, but they are grounded, and since they are attached to my alt fuse, it'll just keep damaging things till I figure this out...


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PostPosted: Thu May 28, 2015 7:10 pm 
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What amperage are the two fuses you are working with? What amperage is the fuse that pops/popped?

How was the alternator tested? Need to be sure the diode voltage drop is proper and you don't have a shorted diode ...

Following the diagram on Pages 78-81 of the FSM electrical PDF, Pages 8-52 to 8-55 in the physical paperback FSM.

Image

Which points were tested based upon this diagram?

I would suggest testing all fuses for continuity with the "popping" fuse location left empty for now. If nothing else went down, then you have a larger current section to look at, versus the smaller sections down the line.

I can't make the diagram any bigger because of windows paint. It is essentially all the "high current" fuses in the engine bay, then leading to the cabin down route "A" the portion off to the right.


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PostPosted: Thu May 28, 2015 8:49 pm 
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I just bought a new alternator tonight because mine was soaked with power steering fluid and definitely wasn't reliable. The alt and battery are currently out of the car.

So, I was able to trace the short circuit to the junction block under the driver side dash. The "fuse +B" is the fuse that feeds the junction block. I unplugged every connector and every fuse and it is still shorting out. Is it possible the junction block itself could short out? None of the interior fuses were blown.


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PostPosted: Thu May 28, 2015 8:56 pm 
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I suppose so. There is photographic evidence from members that water comes in through the harness routed out the passenger side frame rail outer section and into the ECU/floor area (via the harness pass through), but not so much the driver side.

The fuse block would be a rare spot to short out like that. Cannot say I have ever seen it happen yet. But we only represent a small fraction of the cars that were on the road at one time.


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PostPosted: Thu May 28, 2015 9:03 pm 
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The short is on the circuit found on page 8-55 in the manual, connector C58 has the wire coming from the fuse +B from the engine bay, but it also has a white wire as well. This wire is not labelled in the manual but you can see it crossing the connector on the diagram, that's the wire I need to find.


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PostPosted: Fri May 29, 2015 8:09 pm 
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Narrowed it down to the "room" fuse in the cabin which is fuse 8. According to the manual this fuse is for the MPI control unit, Radio, 4 A/T control unit, a few interior lights and clock...


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PostPosted: Fri May 29, 2015 9:47 pm 
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Pull the radio harness off the radio.
Next, pull the MPI relay out from below the radio and see what happens when it gets disconnected.
They are behind the same trim.

Unfortunately that means you have to remove the cover on the bottom of the steering colum/dash (bolts and screws), then the center column upper trim (hidden screws facing up x2), ashtray removal, then a couple screws on the radio and on the MPI unit. May have to take out the center console base (shifter cover etc) because that covers the side of the upper console. I've been in there a few times ....

Could the door switch wiring have been pinched in the floor when a seat/carpet was put back in? Trunk mini light on driver rear panel is wired there, along with trunk light/switch, dome light ... the plot thickens. An internal fault on something like the MPI relay I would vote being the most likely scenario if nothing changed. Pinched wires would usually rear their ugly head quite quickly ... but I hope you find this soon. What a bummer to have to test out ....


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PostPosted: Sat May 30, 2015 8:01 am 
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Don't think anything got pinched, not recently anyway as the only wiring I've done has been under the hood. I can pull the seat and have a look.

So far I have removed the ECU, gauge cluster, radio, dome light, luggage light, clock, and still has the short.

I didn't see any MPI relay behind the radio though? is it directly behind the radio or underneath another panel perhaps? Guess that would be the last thing to disconnect before checking the harness.

Ya this has not been a fun experience, but it has given me the chance to get to know my way around the interior and wiring. Thanks for the help...


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PostPosted: Sat May 30, 2015 9:23 am 
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The relay looks like this:
Image

Should be in roughly a similar position to this picture, following "Y".

Click for tuners thread


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PostPosted: Sun May 31, 2015 1:21 pm 
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Well got it all figured out, the short to ground was intermittent which made it a pain to find, turned out to be in the harness for the rear hatch. When I was welding patches on the hatch to close up the holes I must have melted the rubber off the one harness...

New alternator is in and she is running like a champ. I also decided to delete the leaky power steering system which was the cause of this nightmare and complete stereo as well. Who needs a stereo with a 4g63 under the hood? :D

About to take here out for a spin to enjoy the new steering feel, thanks for the help!


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PostPosted: Tue Jun 02, 2015 8:32 pm 
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SOOOO happy to hear that another one is back on the road.

Come help me wire in some fans. Better yet, buy me some fans. ..... I kid.

I was going to post a while back about tail light housing ground screws loosening and causing electrical gremlins, but figured we were headed somewhere else ....

Spidey sense!


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