HELP! Max A/C, fan on high = FIRE!!

[Wes8398]

I was driving home from work today (10 minute drive at most) and decided to blast my a/c. I had it on "max a/c" and had the fan to high. I rarely do this, but when I do it usually results in my voltage gauge dropping a bit. Half way through my drive though, my voltage gauge was only about 1/8th of the way and my car had started running a little funny (obviously). On my way up the driveway I smelt something and by the time I parked there was smoke coming out from under the hood. I ran and opened the hood to see a small fire on the side of the power distribution box, where the ground and power cables connect to the box. Thankfully I was able to blow the flame out quite easily, but WTF happened??? More importantly, why did it happen? Is it an easy fix?
The black cable (with orange stripe) that connects to the power distribution box melted and is no longer connected, but the car will still start and run. I'm guessing maybe that cable runs to the alternator and is involved in charging the battery...? Until I get some ideas from you guys, I'm not driving the car anywhere in case I need to save battery juice to get it down to the mechanic (if I can't fix it myself).

Thanks in advance.

 

[x182dan]

It could be a bad alternator

 

[GDTrumbo]

WOW! Theres a lot of resistance for it to heat up and burn in that short of a time span. Highly unusual.

GT

 

[JDwhite98gt]

well if u want to do it yourself, i would suggest that first you take off the alt and take it to autozone, gayboys or your local autoparts store and have them test it, replace if needed, then ask them for that cable, i would assume that they already have it precut with the correct terminals in place, if not measure the gauge of the wire and pick up a length of it ( prob better if u get extra just incase). Then install/replace the parts on the car and try to recreate the driving situation while parked in the driveway. Start the car run the AC on max and at full blast. I would be better if you had a partner to watch the voltage gauge and such while you rev/hold at cruising rpm (2000-2500 rpm) the car by hand and watch and see what happens. Also check all your ground cables. Make sure u check the routing of that cable that burnt make sure its not rubbing on any metal that would have caused it to arc and or rub through the insulation.

 

[Wes8398]

I'm not too sure how to repair the link because one end of it runs into looming and more engine wiring, and I can't see how it connects to the power distribution box on the other end. Guess I'll have a closer look tomorrow.

I'm wondering if this fire has something to do with why my battery gauge always seemed to gradually decline when I ran my a/c or defrost ... I don't see any exposed wire anywhere or anywhere that it could short ... and I have no idea why there would have been that much of an electrical load there. Can a bad alternator create a situation like that?

 

[JDwhite98gt]

Yea, if that wire is connected to the alt then the alt is asking for more juice (draw) and its overloading the wire creating too much heat and heat makes....fire. So, yea start digging into that spaggetti and trace where that wire goes. take off all the tape on the loom remove it and trace the wires...it sounds scary but its not once you get ur hands dirty. If it doesnt go to the alt then just find where and go from there. I know my ac draws a lot of current, my gauge will go all the way down but stay in the "safe" zone on the gauge, especially when stopped at a red light with my foot on the brake, radio on, all that good stuff but it will rise slightly when I'm cruising.... its happened with all of my sn's.

 

[Willis_98GT]

subscribed, good luck

 

[Wes8398]

I didn't want to dig too far into it tonight (lack of daylight when I finally got at it) but I did a little tinkering with my volt-meter. With the car off my meter's showing battery voltage of 12.32. When I turn the car off (no lights or a/c or anything) it reads about 11.90, and when I turn the a/c on it reads about 11.65 to 11.80 depending on the fan speed I select. And this is all with that one black wire totally disconnected from the power distribution box. What all that means, I'm not too sure, but my battery gauge isn't agreeing with the volt meter ... it's still pointing to about the "N" in "NORMAL" on the gauge.

I'll attempt to attach some pictures. I should mention that I also took the (half melted) cover off of the fusable link side of the power distribution box. It's a mess and I can't even get that little 13mm nut off ... cracked my fuse box a bit while trying...


Pictures...

 

[JDwhite98gt]

Yikes! yea that nut is hard to get off, I've tried once before too, forget what for but I had to give up before I cracked the housing, I heard it make a noise and stopped, said fu*k that. well I'm subscribed so let us know what the deal is when u dwell deeper into that wiring.

 

[CC'S95GT]

Corrosion inside the insulation would cause extra resistance and cause the wire to heat up enough to catch the insulation on fire. Either replace the gnd wire with new cable. Or cut the wire back far enough to get to clean wire and replacement the connector.
Everything still works because there is lots of gnds. but that doesn't mean you don't need it.

 

[Wes8398]

Corrosion inside the insulation would cause extra resistance and cause the wire to heat up enough to catch the insulation on fire. Either replace the gnd wire with new cable. Or cut the wire back far enough to get to clean wire and replacement the connector.
Everything still works because there is lots of gnds. but that doesn't mean you don't need it.

Are you convinced that's a ground, and not the cable from the alternator? From the volt meter readings above, it doesn't appear to be charging with that wire unattached...

 

[mach1197203]

The ends of the wires that attach to the power distribution box have fusable links on them. This is not just replace the wire and all is good, these fusable links need to be there that is what burnt up. From looking at your vehicle tag the alternator has been off of the vehicle at least once. Check the main plug on it (black one), the piece that folds over on it and tabs onto the regulator on the alternator may have a crack in it. If this is the case it is probably vibrating loose a little bit and causeing a short. This is a common problem with all ford alternators that use this style plug, they are very easy to crack and cause problems down the road. You can buy a replacement pigtail from ford for around $15-$20. Most wont have one in stock but they should be able to get it fairly quick. Also the ground strap that runs by the oil filter (braided), go by your local Autozone and get a new one out of there help section, befor you put it on get some liquid electirical tape and put a good few coats on it this will help it last longer down the road. The 4.6 motors are bad about fraying this strap when the Motor mounts start to go bad (engine torque over). Let us know how it turns out.

 

[Wes8398]

Well I brought the car to a very reputable shop in town, since I don't have a soldering gun. The mechanic gave it a once-over and said there was no reason for there to be a fusible link there but he'd take a closer look at it and give me a call. He called 1/2 an hour later and said he'd fixed it up. It looks like he just cut the fusible link portion off and put a new connector on the end. I questioned the lack of a fusible link there and he said that he didn't see why I'd need one. I told him that I had heard contrary info, but he was adament that a fusible link wasn't needed there. I can't remember his explanation word-for-word but he said that the wire was power coming straight from the alt and powering the accessories and charging the battery via the "power distribution box". He said that wire could in fact just run straight to the battery, but in this application obviously doesn't.
He ran the a/c on max for quite some time without any issues and he also verified that the alternator was doing it's job just fine.
I have to admit that from the info you guys have provided, I'm a little uneasy with the "repair", but everything seems to be working fine... Not really sure where to go or what to think from here.

 

[mach1197203]

Well it works. You need to get those fusible links back in there though. Ford put them for a reason. Those links are there to protect the alternator system from burning up the rest of the wiring, if the bridge in the alternator goes out and fuses the diodes together the alternator can run rampant on the elctrical system. From the sounds of it the "mechanic" is no mechanic or he would have know this. In the older cars this was not needed but that was before there where cars that had such high electrical demands. I will get back to you on the size of link that is supposed to be there as soon as I can find it. They are easy to put in but you will need to solder them in. Did you check the plugs for the craks in them?

 

[Wes8398]

Well it works. You need to get those fusible links back in there though. Ford put them for a reason. Those links are there to protect the alternator system from burning up the rest of the wiring, if the bridge in the alternator goes out and fuses the diodes together the alternator can run rampant on the elctrical system. From the sounds of it the "mechanic" is no mechanic or he would have know this. In the older cars this was not needed but that was before there where cars that had such high electrical demands. I will get back to you on the size of link that is supposed to be there as soon as I can find it. They are easy to put in but you will need to solder them in. Did you check the plugs for the craks in them?

Well, he is in fact a very reputable mechanic, but I also doubted him on this. I brought the car over to a local shop called "Universal Auto Electric" who have been around for decades as THE go-to auto electrical people. After I explained everything he was adamant that a fusible link needed to be put back in, but then he came out and actually looked at my car and changed his opinion. If I can't trust what he says, I can't trust anyone. His point was the same as the original mechanic's point (and many others who have agreed with the mechanic); the wire is going to the FUSE BOX (aka the protection for the rest of your electrical system), so why put a fuse in front of all those other fuses...? If the alt goes haywire and starts spiking amperage, etc - those fuses will protect the rest of the electrical system.

I have to say that I'm now pretty much convinced that it's fine the way it is ... unless someone can sway me again. haha

 

[mach1197203]

When the fuse box melts let me know I know where to get you a new one for less than $200. Oh yeah watch the battery for side buldging. Batteries boiling make a big mess. Good luck with it.