Alt. signal wire

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Raider L

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Last night I posted a problem I had with the alternator signal wire up on the ignition switch frying, like it must have caught fire because it was melted to a bunch of other wires it was touching in the bundle. Well, they are mostly all okay after I had a chance to unstick them yesterday and examine them all from the firewall to wherever they all went. So I unplug the black plug up on the ignition switch and pull those wires over the steering column so I could get a clear look at what was going on. Looking at the schematic it shows that a #12 orange wire, (ign.#3) and that signal wire are on a terminal end together in the plug. Also, yesterday I uncovered the wires that go to the bulkhead block that pass wires through the firewall to locate the alt. signal wire and do a continuity check on it to make sure the one I was testing was the one that wnet to the alternator, I have a two wire alt. On that black plug there is the #12 orange (ignition needed at start), #12 red (same), and a little bitty #20 brown wire which is the brake warning switch (ign. #3 same as above).
Yep, that #16 brn. wire was the one. I just wanted to verify that it hadn't gone up in smoke when the one inside caught on fire. No, it was fine. All the engine compartment wires are perfect. So back inside the cab. Today i got all my detailed paper on the wiring of the truck, by the way I have a '74 C10 all hopped up and modified with full Autometer gauges and i rebuilt the whole truck from bumper to bumper frame off. I didn't mod. the wiring other than taking every single wire removed the factory tape and cleaned all the wires from start to finish, and aircraft style reorganized all the wiring and put plastic corrigate on all of it except under the dash, from bumper to bumper. That was all back in 1995-'96. Everything has been perfect up to now.
Today looking at the schematic's and detailed drawings I determined that I don't think that little air compressor had anything to do with that one wire catching fire.
Now here's where I need ya'll's help. That one single wire catching fire was either a problem with the alternator, or the ignition switch. What do you think, and why? But I can't figure why would that one wire catch fire when no fuses were blown, no other wires caught fire although when smoke started coming out from under the dash a block from the house, I pulled over, got out and looked under the dash. The first thing I did was grab hold of the ignition wires, I don't know why, that come out from the fuse block and go up the firewall in a group, I did mine that way to be able to identify those that go to the ignition switch, and up to the ignition switch. When I did, that whole group of wires was hot!! But as I discovered the only wire that actually got hot enough to burn was the alt. signal wire. None of the wires looks like they got hot enough to distort the insulation, turn brown/black, or any other sign of heat. Just the alt. signal wire.
What do you all think could have happened and why because I'm either going to have to replace the alternator and/or the ignition switch as well. But what do you think could have happened and I'm sure it's because I don't fully understand the operation of the system and I've been studying all day and I still can't figure it out. I understand it well enough to trouble shoot most problems but this problem doesn't make any sense at all.
 

Raider L

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Have you seen how small a #24 wire is? The wire coming from the alt. is a regular #16 multi strand wire. The #24 going up to the ignition switch, which I can't see has much of a application in a 12v system, is a single copper wire. It measures .015" in diameter. In the stock instrument printed circuit coming off the same hole in the bulkhead plug as this tiny wire is the wire going to the "gen" light and it is the same size wire coming from the alternator, #16. So, what is this .015" wire supposed to do?? And it's attached to a #12 power wire on the ignition switch that takes starting power in the "start" and "run" position. And it was the one that caught on fire?? And you say, It's only 12 volts. Oh yeah? Stick your tongue on the starting switch and let me crank my truck and see if you don't pee your pants.
 

Raider L

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@SirRobyn0
Read above posts on strange wire fire and tell me what you think.
So, me and my son went out to our local wrecking yard today to see if I could find a car or truck around my year, '74 C10 to see if I could find that alt. signal wire I could get. They had, to my surprise, a '75 Monty Carlo, and two (2) old C10's like mine. In my wiring spares I have every color and size wire in my truck, but now that I'm thinking about it I may need to go back out there and get some light blue wire, I don't have much of that but I do have plenty dark blue wire. But the two colors I don't have any of is brown and tan and tan with a black stripe. So I got two pieces about two feet long each of #20 tan with a black stripe. And I got about two feet of #20 brown wire. Since the schematic shows the alt. signal wire to be #20 tan wire that comes from the wire block on the firewall the two pieces I got will work for them. One will go to the new alt. signal light, red, on the instrument panel next to my volt meter, I could not find that alt. signal #24 tan wire going to the ignition switch plug in any of those vehicles. It was a #16 tan wire although there is another tan wire in that black plug already there in my truck, along with that #24 alt. signal wire that is in the same connector with the #12 orange wire. I don't think GM put that wire in those years vehicles. It wasn't in the Monty Carlo and either one of the two pickups. Oh yeah, I also found a '92 Suburban and it didn't have that tiny signal wire in it's wiring either. So what gives people??
 

SirRobyn0

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@Raider L I'll give this my best shot. I'm going to quote you and answer in italics, to make it easier.

I'm going to preface this to say I don't think I've ever run into your problem, but I'll do my best.

You said "That one single wire catching fire was either a problem with the alternator, or the ignition switch. What do you think, and why?" I'm going with the alternator, and here is why. If the ignition switch was having a problem the power wire into the ignition switch would be what's melted. The signal wire supplies a small amount of electricity to the alternator to get the electromagnets working. Possibly if a electromagnet was shorting out it might overload that circuit. Might not be a bad idea to do a continuity test from end to end on that wire if you haven't already.

"Have you seen how small a #24 wire is? The wire coming from the alt. is a regular #16 multi strand wire. The #24 going up to the ignition switch, which I can't see has much of a application in a 12v system, is a single copper wire. " That make sense as to why that was the section of wire that burned up. The smaller wire couldn't take the load, but the #16 could, or the #24 fried out before the #16 had a chance.

"I don't think GM put that wire in those years vehicles. It wasn't in the Monty Carlo and either one of the two pickups. Oh yeah, I also found a '92 Suburban and it didn't have that tiny signal wire in it's wiring either. So what gives people??" I don't have an answer for this, but I think I know what I'd do. That terminal on the alternator needs 12 volts, I would make sure it gets that. You can always replace that tiny wire you couldn't get with something larger. It wouldn't be factory but it would function, or omit it and see if the system functions without it.

If you don't find a short to ground, then I feel strongly that the alternator set this off and should be replaced. I don't think that the volt gauge could cause this, but it is something to keep in mind.

Hopefully something in there helps. I'll watch your thread and I'
m more than happy to try to help if I can.
 

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I'm not 100% sure but I thought the brown wire aka "exciter" wire was a resistance wire. It "senses" but doesn't really carry a load. That's why its a small gauge solid strand. If the regulator went wacky and started overcharging I could see that wire getting hot enough to melt. I remember dealing with that wire years back when I converted and upgraded my electrical system. I know I ended up removing it but am a little foggy on the details.
 

SirRobyn0

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I'm not 100% sure but I thought the brown wire aka "exciter" wire was a resistance wire. It "senses" but doesn't really carry a load. That's why its a small gauge solid strand. If the regulator went wacky and started overcharging I could see that wire getting hot enough to melt. I remember dealing with that wire years back when I converted and upgraded my electrical system. I know I ended up removing it but am a little foggy on the details.
That would make sense.
 

Raider L

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@SirRobyn0
Man, thanks a lot!! I was considering changing out that alternator, I have a new spare, put it in and see what happens. And yeah, I did do a continuity test and it was good.
@SquareRoot, Huge thanks! I was thinking of doing the same thing by removing it and see what affect it had on the system. Anything to keep from seeing smoke from coming out from under my dash going down the street!! Omg! You can't imagine the panic because I knew if it was something real serious I only had fractions of seconds to analyze the situation before real fire started... I did not want to see my truck on fire a block and a half from the house!!
I keep going over the electrical schematic. Today I discovered that one of the power wires that goes to the heater fan speed switch, #14 BRN (brown)-50, which is the number in the circuit, is the wire that goes to the other end of the fuse that goes to the #12 orange wire, also the #24 signal wire on it, that goes to the ignition switch. In that circuit power goes to the #12 wire and supplies power to the fan switch when the engine is in "start" and "run". That fan switch has been out for some time now. I thought that maybe it's shorted out and backed up 12v to that #12 orange on the ignition switch? Before I restart the truck I'm unplugging the fan speed switch (it's out anyway and needs to replaced), and in the fan circuit is the three spring resister if some of you guys who still have A/C know, it's in the box that sticks out over on the left side of the eng. compt. I think that has the evaporater in it? I'll unplug that to cut out the heater fan circuit altogether. That way the only things left in the ignition system will be the alternator, the starter, and the ignition switch. If the wiring gets hot I'll at least know it's one of those three.
 

Raider L

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@SirRobyn0
Thank you. Today I studied the wiring schematic some more trying to understand the relationship of the alternator and the other systems together. In the starting system should only involve three components, the battery, the starter, and the ignition switch. The alternator doesn't even come in until the engine is running. I mean this is all obvious. But there are wires that are incorporated like that little signal wire. When, like what you said something in the alternator went out or had some kind of problem, and I still think something happened when I tried to run that air compressor, some current got involved because it said not to use the 3 volt cigarette lighter type system but to use the 10 volt power point system to run the pump, over loaded those wires going back to the ignition switch even though everything was off. Just because it's off doesn't mean juice isn't going through the system and obviously over loading something. I am going to go to the wrecking yard and pull a power point from a newer car and wire it in seperately just for anything outside the system I have. I do have a 750 watt inverter you can hook onto the battery and run 115-120 v household anything off of, but it's hooked to the battery direct not the cigarette lighter.
I suppose the first time I started the truck after using that pump set up the alternator and it's signal wire for failure. And 30 seconds after I shut the engine off at the house then cranked it up again did it in. But it still took a minute or so to actually heat up and then catch fire.
And when I reached under the dash and felt the wires going to the ignition switch and they were hot, that's what I was studying today. I wanted to know why. And there are a couple of wires in that bundle that the alternator would have a over heating affect on. The #12 red wire coming from the alt., and the #12 purple wire that goes to the ignition switch from the neutral safety switch, and obviously the #12 orange wire. If there was something going on in those wires that big of wire would be more than enough to heat up the whole bunch of wire.
I'd guide you through what I found but it would be too much writing. Just suffice it to say I think I understand it better now since I've been studying the schematic for the last five days and thinking about more the why than what. That part is obvious, but it's the why that is more important to understand. That way I won't be making that mistake again.
Like most everyone I don't like electrical problems. I didn't like them when I worked on aircraft, as most of the other mechanics didn't either. It's because you are forced to go back to basics to understand the "why". There can't be smoke in the passenger compartment while flying because you may be a long way from setting down if there is.
At least I was a block and a half from the house.
 

SirRobyn0

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@Raider L A while back at the shop we had a truck it was a Ford with a triton in it. I don't really work on the cars in the shop on a daily bases anymore. I turn a wrench if the techs get overloaded or if one of them calls out, or something comes in that they don't know how to fix. It just hurts my body to much to be under a hood all the time day in and day out. Anyhow, this Triton comes in and it's had a rat or something in the engine compartment that chewed up a bunch of wires. One of the guys asked me to look at, after he'd cleaned up the mess because apparently I'm the shops "12 volt electrician" I told him if that's the case we are all in trouble lol. No I don't like electrical especially on the newer vehicles.

What I like about our old rigs is that they are so simple in basic theory. Alternator needs the main "big" charge wire, and 12 volts turned on at both the other terminals to excite the magnets and charging occurs. But still the systems can be complicated with all the added wiring that can be sometimes hard to understand like what you are going though now.
 

Raider L

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Well, let me see if I can remember how to load photos.

Here's what happened to the 12v wire as soon as I tried to pry off the boot. Suddenly the whole wire came with the boot! I know it's a bit blurry, new camera I'm getting used to.
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The photo below is of the alt. signal wire that fried. That other tan wire is the brake warning light wire at 20 t(tan)/b(black stripe)-33, (actually the schematic says it's a black wire with a tan stripe but it's the other way around in my truck), on the schematic which goes to this plug which is Ign. 3.
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Sorry for the blurr again. I was trying to get a shot of the melted insulation on the wire.
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In the photo below you can see how hot the 12v bolt got. That is a brand new bolt. This alternator I don't think has been in the truck 6 mos. with all new parts including a new rotor. I guess this is what you get with sorry Chinese parts.
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Raider L

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The photo below, now you have to orient yourself to the picture, the right side is the bottom of the wire block going towards the floor, okay? Lean your head to the left, ha, ha. The pencil is pointing to whats left of the alt. signal wire. The light green wire to the right of it is the right side of this wire block. And that small gray wire is to the left of the signal wire. I think what the factory workers did was the engine compartment guy tells the interior guy, "Here's a wire." And just pushed it through anywhere through any hole. And so on and so on for each wire not paying attention to where it's supposed to be in relation to the schematic. The engine compartment wires are not in the right holes. But they all are going to where they are supposed to be and where they are supposed to go. That's what angers me the most. It's screwed up, but it's right.
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This is the stator. You put one ohm meter probe (red) on the frame and touch each terminal up there with the other one, (black). I think, if I'm reading the instructions right, if there's no reading it's okay?? What does "open" mean? And does "grounded" mean you'd get a reading? See, here I worked on jets and I still get it mixed up. Anyway there was no reading from the stator.
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Below is what the rectifier looks like. You place the red probe on the finned metal part then you touch the black probe on the metal piece surrounding the threaded post but not the post just the square metal part around it. It should read low. Then switch the probes, black on the finned metal part and red on the square metal part around the post. It should read high. If they are both the same or not a reading on either one the rectifier is bad. Do both sides of the square metal parts around the screws from each side. Check this sites archives for details if you need to see instructions in writing, recommended.
Oh yeah, see the 12v screw above the rectifier bridge upper left, see how shiny and new it looks? That's the part that was on the inside of the housing. Just the part that was outside the housing and had the wire connected to it got burnt. What happened there? Maybe a bad wire somewhere? I am going to unwrap the wire all the way to check it out.
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Below is the diode trio. Touch the red probe on the long leg and the black probe on any one of the three ring looking connectors. Do all three one at a time. I think there should be no reading?
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SirRobyn0

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@Raider L I can't give you any feedback on the internal readings you got testing the alternator as I've never rebuilt one. I've pulled them apart to replace diodes, but that was diagnosed based on a bad diode pattern with the engine running and telltale flickering for lights.

On your second picture. The small wire that is single stranded. Have you been able to figure out the purpose to that tiny little wire? And is it wrapped around the larger wire.

I seriously think if it was my truck I'd install a new alternator. I'd assume at 6 months old it's under warranty, so why not get it swapped out for free. I'd then fix the melted wiring and fire it up and monitor the system. BTW, I enjoyed looking at the pictures. Kind of makes it easier to follow along.
 

Raider L

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@SirRobyn0
Well, today I went out to the truck and after climbing into the engine compartment, you know some of our truck you could stand down on the ground, ha, ha, anyway and took all the old corrugated cover and old electrical tape off in places enough to be able to remove the conduit so I could actually look down at the firewall wire block, pull on some wires and see what was what from the alternator down to that block on the firewall.
But looking at the schematic I discovered that when I was redoing the wires for my new Amp. gauge I mistakenly did not replace the "fusible link", which is nothing more than a small wire soldered to a big wire. It's so if something over volts or amps it'll burn up the smaller wire before it gets to something else. In my case the #12 red wire that comes from the alternator goes up to a splice, and one leg becomes a #16 black wire, the fusible link, goes to the junction block, and the other leg of the splice is a same #12 red wire that goes inside the cab to the fuse panel to power stuff inside the cab.
Well, I didn't put that #16 black wire to the junction block but rather just continued the #12 red wire to the junction block. This may over time could have been the cause of the signal wire burning up, and the red wire bolted on the back of the alt. to burn up as well, as I found last night.
Speaking of that since you asked the #16 brn wire comes off no. 1 on the alt. as a "exciter wire" I would suppose. When it comes out of the wire block inside the cab there are two wires coming from the one block hole. One wire is a continuation of the #16 brn wire and it goes to the instrument panel as that red light that comes on when you crank the truck. The other wire that is in the same block hole is the #24 brn wire signal wire that goes to a #12 orange wire at the ignition switch to tell the alt. the engine is in "start" and to energize the field windings that makes the alternator do what it does, to charge the battery.
So far I really haven't discovered anything that looks like it was the cause of that signal wire burning up......yet. Tomorrows another day. I think that I may have had that fuseable link wire not the right size for one thing and something about plugging in that air compressor into the system that may have somehow over loaded the electrical system, with the engine off....somehow.
Unless someone looking over this thread might have a better idea about how that signal wire got fried.
Hey, you really ought to start rebuilding your own alternators. It's fun and educational (ha, ha). But at least you'd know you did it and it was right. I opened up a box with a brand new alternator in it I had in spare parts tonight and found all the screws on the brush block and voltage regulator completely loose. I had a note on the box to change out the voltage regulator to one with a higher rating. I don't like the new ones with only 14, or 14.2 volt output. Because when you have everything on the voltage drops down to 13.8 volts or I've seen 13.6 volts. And that will mess your alternator up to. I like the regulators of 14.6 volts specifically. You can turn everything on and it will read 14.2 on the gauge. The 14.8"s are to high. But the 14.6's are getting harder to find.
 
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SirRobyn0

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I've thought about learning, use to be a local guy that we'd use from time to time, but he shut down a few years ago.
 

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