I just picked up a 86 4runner yesterday that is in pretty good condition. The only problem it has is that it keeps blowing the15 amp 'engine' fuse in the cabin, which disables the back power window and the gauge cluster. When it blows the charge light comes and and i've been told that it also doesn't charge the battery anymore at that point.

The guy I bought it from had the alternator recently checked out and it was fine. While looking around the engine bay the only thing I noticed was that there was a loose black wire sitting in the engine bay. I traced it back to the plug with 4 connectors. There was a yellow wire, red wire, white wire and a black wire. The yellow, red and white all go straight to a plug on the alternator. Is the black wire just a ground wire? Thanks


Patrick
1986 SR5 4runner

 

That wire should be a ground wire that goes to the block. Does is have a round connector that you can put a bolt through on it? According to the 1987 FSM, the engine fuse goes to:

Combination meter
Power window relay
PPS computer
Neutral start switch and ECT computer
O/D off indicator
Back up light switch
Alternator - Red wire

A short in any of those circuits could blow the fuse. If the alternator was just checked for voltage output, then it was not properly checked for the problem you are having. If I understand alternators correctly, then the output goes through the 'Charge' fuse to charge the battery. The 'Engine' fuse just sends current to the alternator when the ignition is on to basically turn it on.

 

The black wire didn't have a ring terminal on it, but I just put one on and bolted it up to the block.

Is it possible to have a short inside the alternator or voltage regulator? I checked most of the wires without finding anything. The problem is intermitten. I'd say I blow a fuse every 20 miles or so. After driving the car I noticed some other things I figured I would mention, only the charge light comes on, never the brake light. Also the other day while going up a steep hill the charge light came on momentarily but it didn't blow the fuse. Any ideas? Thanks for the help

Patrick
86 4runner SR5

 

My 85 truck just had a similar problem, fuse for the guage cluster kept blowing. It turned out to be one hell of an electrical shakedown (there was some other really bad hack job wiring from previous owners). Eventually I traced it back to the Alternator as being the root of the cause. I pulled it, had it tested, failed, put in a new one, and so far no problems.

My suggestion would be to yank the alternator, take it to Checker or some place, they should test it for free. It's worth it in my opinion, only takes 20 minutes to yank it. I'm assuming it's similar to my 85 (I dunno how much the IFS reworks things), so you'll have to drain the coolant, pull off the lower radiator inlet hose, then you can drop the alternator from the bottom.

 

Actually, you won't need to drain the coolant, pull the hose, etc. But, if it makes it easier, then sure. I've never had to, though.

Somewhere you have a bad connection and enough heat is building up to blow the fuse. Check out all of the wiring, of course. But, also check your ECM for any corrosion.

 

Getting the alternator tested is a good idea. The store is most likely going to just check for voltage output, so you might need to take it apart and check for shorts or loose parts. The FSM has the procedure for taking it apart and testing all the parts inside of the alternator. It is not difficult to do.

 

You're probably right. I recently pulled mine on Saturday night, about 8PM. I was in a hurry to get it buttoned up for a Sunday wheeling trip (which didn't happen anyway). I figured from looking at it, it was easier for me to drain the coolant and pull the one hose (which takes about 5 minutes) than struggle with the thing to drop it out for who knows how long (sometimes it falls out, sometimes they fight you to the very end!). It didn't hurt to flush the coolant in my case, anyway.

 

When the charge light stays on it means your alternator is going bad. Easy replacement on your 85. check it again.

 

Does the back window work correctly prioer to the fuse blowing? A motor stuck on draws a lot of current.

If you let the truck idle in your driveway, will the fuse blow?

If no clues from the above, I'd get the wiring diagram and check what is fed through that fuse.

It sounds like an intermittant grounding of a 12v line that goes somewhere else in the truck. Hence the wiring diagram to check for chaffed wires. The point of the short will be obvious if you find it.

If its a motor-on that you don't know about, that is a load problem that will only produce heat at the motor before the fuse goes.

 

I'd look for a little while for the problem but if it turned out to be hard to find, I would go redneck on it.. Ac delco and put a flip switch on the the things that i needed to work and do away with the fuse all together,,, but thats just me

 

I just replaced the alternator and everything seems to be fine now. It must of been a short or something in the alternator/regulator. When I pulled the old alternator out it was covered in oil. When I bought the car the valve cover was only held on by 3 bolts, 2 of which were hand tight.

Patrick
86 SR5 4runner