Cdsbigsby

Hey guys, I'm new here, first time poster but this forum has helped me out with countless problems - I google my problem, 99% of the time I find my answer here.

But here's my latest problem - my '86 4runner was sitting at work a few weeks ago while I was out driving around in my company van, so it was off with the keys out of the ignition, and it had a small electrical fire on the back of the alternator, right where the plug goes in. luckily a coworker was standing right there and unplugged the battery before it got too bad.

What would've caused this? I know almost nothing about electrical systems but I'm thinking voltage regulator?

From what someone's told me, I was planning on having the alternator bench tested, getting a new voltage regulator, and replacing the crispy wiring. Anything else I should look for?

Thanks a lot

Terrys87

iTrader: (1)

Do you have a power steering leak? I had an alternator fire due to a PS leak.

Cdsbigsby

Not that I'm aware of. How do you mean, the ps fluid drips onto the wires, causing a short?

osv

I do wire welding with a goweld, powered by a couple of car batteries... it'll throw up a spark :-)

point being, batteries have tremendous energy potential, more than enough to melt steel... if something connected to the battery was on fire, it could be more than just the wiring you see that's burnt.

what I don't get is why a fuse didn't blow when it shorted? looking at an '87 fsm, the battery juice goes through a high-amperage fuseable link(??), straight to the ignition key, and then to the alternator.

so if the ignition key is off, there shouldn't be any current going beyond that... but one side of it will always remain hot, waiting for the key to be turned.

you said that the ignition key was off, which should have meant that there wasn't any juice at the alternator, so how did it short out?

the other day one of the old timers out here pointed out that you can essentially pull the ignition key out of the steering column while the motor is running... which means that if you turn the key to where you think it's off, but it's not completely off... perhaps there is juice at the alternator?

or possibly the ignition switch itself shorted out, even when it was turned off.

do your homework on this, maybe consider taking it to an automotive electrical shop if you aren't comfortable working on electrical.

osv

if i'm reading the schematic right, the only way that there could have been a fire from the power steering fluid is if the fire started while the car was running, because turning off the ignition key should have killed the juice to the alternator.

i'd really like to know what happened here! good luck, please let us know how it turns out.

Terrys87

iTrader: (1)

On my fire, I was driving down the road and seen smoke. Before I could get pulled off of the road the truck just died. I popped the hood expecting to see steam and the alternator was smoldering, after a few seconds it broke out into a small flame. Luckily I had a 44 once drink to extinguish the fire.

I had a friend to bring me a new alternator and installed it on the road side. I could tell there was power steering fluid everywhere. After installing the alternator it, it was completely dead. The 80 amp fuse eventually did blow but not until the fluid had caught fire and shorted the wires in the alternator is my best guess.

I changed out the 80 fuse, replaced the power steering line, (high pressure line if I recall right) and was on my way again. It was a scary situation, but luckily there really isnt awhole lot on the drivers side area of the motor for anything else to catch fire.

Because of that situation, anytime and everytime I am working on the power steering, I use a one gallon freezer bag to cover the alternator and disconnect the battery. It may seem like common sense now but really how many think to do it or have thougt that there is no need to disconnect the battery for a power steering issue. I will admit that I never disconnected the battery when working on power steering.

Since then I covered all of my alternators when removing the pump and such and guess what gets coated with the fluid. Luckily the bag took the brunt of it. Before that situation it never happend to me. Now anytime I look at the power steering assembly the covered alternator gets soaked.

osv

good info about that power steering fluid burning, reading this thread is making me nervous! lol

Terrys87

iTrader: (1)

LOL...I removed the last paragraph, hope that helps some, but try it in the salvage or on friends trucks. You might be suprised.

RAD4Runner

Look at schematic (see my sig) of charging system:

• Thick white "B" wire connected to alt screw-post will always have 12V because it is directly connected to Batt plus, regardless of state of ignition switch. IF you have a bad rectifier inside the alternator, power may make it's way to the winding.
  
• Thin white "S" wire in connector that plugs into alt also has 12V because it taps off the "B" wire near the fuseblock- no disconnects at all from battery. Some conductive liquid (plain water plus dirt, or oily liquid with dirt) could cause it to arc and ignite the oil in there.
  

Somewhere in the forum, I posted a quick way to check for bad (shorted/leaking) rectifier, with power off. Need to disconnect thick white "B" wire from the alternator post (screw). Then measure resistance of post to ground. Sorry I forgot what resistance you'd want but is rather high- somewhere in the high mega-ohms.

osv

you are right, it does bypass the ignition switch, which is logical, because you wouldn't want the entire output of the alternator passing through the ignition switch... that's what I get for typing at midnight, lol

so a power steering fluid spill, or similar, could have been a factor here... maybe this is a good time for the o.p. to do a full inspection for spills.