Hello all, and thank you for reading this. This 86 4runner is my daily driver, recreation vehicle, and one of my favorite things in life. I have been battling an electrical issue with a wide variety of confusing symptoms over the last 2 months (2300 miles). I normally try to figure things out for myself, but this time i'm at the end of my rope, and i need help. It started during a road trip when i turned the key and nothing happened - no indicator lights lit up, no noise, nothing. Oddly the dome light was not getting power when this happened also. This happened a few times on that trip and it always suddenly started working after sitting for about 30 minutes. This stopped happening once i got home, which i attribute to climate - i live in a dry part of alaska and my trip was to a coastal community where there is likely much more moisture in the air.
Next I realized that my battery was slowly getting drained. I checked all the grounds under the hood as instructed by this website and i made new ground cables to the block and body. I've tried 3 different batteries, and inspected and cleaned up a variety of connections under the hood and in the passenger compartment as recommended by a number of threads on this site.

To make a long story short, i just realized this last night: With the engine running i get about 13 volts at the battery with no lights or accessories on. When i disconnect the negative battery cable i get about 14.7 volts (see photo). To me, this indicates that the alternator is functioning properly, but there is a bad connection somewhere causing a voltage drop. Can anyone think of anything specific that could be causing this?

I'm appreciative of any info anyone can provide.
Jeff

 

Your "dirty" grounds have nothing to do with your battery draining, in fact ohm's law states the higher the resistance the lower the current!

What you need to figure out is what subsystem is pulling power from the battery with the key off. You do this with your meter set to current measurements (amps) wired in series (red lead to battery, black lead to positive battery wire terminal) and start pulling fuses from the distribution block under the hood untill you find the high current (>=100ma) draw.

 

Disconnecting the battery while running was something you could get away with in the '70s, with no computers and mechanical voltage regulators. With the electronics in "modern" (when was the last time you heard of 1986 as modern?) cars, you run the very real risk of damaging a very expensive electronic component.

13.9v running is fine (at 25°C). http://web.archive.org/web/201102051.../2onvehicl.pdf When you disconnected the battery, the voltage regulator sensed "zero" volts and jumped up to 14.7v in an attempt to charge the "low" battery.

If you're really getting "about" 13v, you probably have a problem with the voltage regulator. Having trouble charging the battery, it's leaving the battery "low." Down here in the lower 48 just about any auto parts store will check your alternator (including the voltage regulator) for free. You might want to first check the price on a reman alternator from (say) RockAuto. The reasons you can get a "free" check is they hope to sell you a replacement; knowing the alternatives in advance will help you to make a decision.

 

When the problem occurred, what was your battery voltage?
I help you you help me Please measure resistance from alt "B" terminal stud to ground (alternator body):The last time I did this IIRC, I got double-digit meg-ohms. On my new Reman Denso, I'm getting 70k-ohms. This affects current draw below.

This^^^ my draw with ignition off WAS* 20 milli-amperes. *Before I replaced my alternator. Will measure again later.
Illustrated here.

We have a thread on sources of Denso alternators (here). I got best deal from NAPA, but am asking O.P. and fellow members to help check "B" stud terminal resistance to ground (above).

 

Thanks you all for your replies.

Thanks! That makes total sense. I ordered a Denso Alternator from Rock Auto - for once I don't mind just throwing a part at a problem without being 100% sure it's bad. I've already gone through 2 Autozone alternators in the last year (Duralast #14668) and I should have just bought a Denso a long time ago. Hopefully this fixes my charging problem, but it seems like i still have an electrical gremlin waiting to show itself. My original problem (intermittently no response when turning the key, and no dome light) shouldn't be alternator related.

 

12.3V is pretty good, I'm able to crank strongly even below that. However, a better practical test of battery health OR quality of connections is to turn on heavy loads (lights, blower, rear window motor, after-market audio amp blasting Eruption- May Eddie Van Halen rest in peace). Measure AT THE BATTERY POST ITSELF.
1) If battery voltage drops significantly, then battery is weak or has low charge.
2) If battery voltage does not drop at all, then you have high resistance between posts and the loads - most likely between battery and fuse block.

 

I just took her for a drive and experienced a bunch of really confusing symptoms. I'll try to be brief, but there's a lot going on. She fired right up - no signs of a weak battery. A couple miles later the radio shut off, then the clock, then i noticed the gas and temp gauges weren't even getting power. But she was still running fine. I turned on the headlights just to see what would happen and the engine stumbled and the clock and radio came back on. I turned the lights off and everything started to flicker (the clock and several indicator lights) like it was possessed. I pulled over and swapped out the battery with a fully charged one i had for the occasion. Turned the key to start it and nothing happens - no noise, no indicator lights come on, and no power to the dome light. However the headlights work. I sat there for about 15 minutes and she suddenly came to life and fired up like normal and i stumbled and flickered my way home.
Does any of this make sense to anyone? I'm gonna have to park her until i figure this out.

 

I REPEAT:
https://www.yotatech.com/forums/f116.../#post52452023

 

I would start with some voltage tests.

Battery post to battery post.
Engine running, battery post to battery post.
Engine running, head lamps on high, battery to battery post.

Now they get tricky!
Engine off, high beams on, negative battery post (ground wire of meter) to fender ground wire lug.

You're going to repeat this one to the bolt that holds the wire, and then again to one of the bolts or bolt holes aft of the ground wire on the fender area.

This is a loaded circuit voltage drop test. It identifies high resistance wires and junctions.

Now repeat these tests for all the ground wires (refer to the ground point thread for the 22re for images) while triggering loads like the head light stereo and blow fan. One in each kick panel, on to the fire wall, one to the right hand engine mount, one near the alternator power-steering distributor area, and one near the center of the dash.

This should turn up several wires that need replaced or junctions that need cleaned and tightened up.

One more check is the voltage drop across the battery positive post to the big fuse in the distribution block in the engine bay.


Now you might be thinking, "well I'll just unhook and clean them all", don't do this without testing them. If you clean and reconnect stuff without testing you don't know that you have identified and we're able to rectify problems. You need quantifiable results like " I was losing half a volt here, but now I'm only losing 0.01v" it's important!

 

Thanks Co_94_PU for running through those voltage drop test procedures for me. I got halfway through and discovered the problem was in my main fuse box in the engine compartment. The plastic housing that holds the 80 amp fuse was melted.


Not sure what caused it, but it looks like a previous owner replaced the fusible link (that is supposed to get power from the battery to the headlights, ignition, alternator, etc) with a 14 gauge wire - and that worked fine for years. I'm really surprised such a small wire could handle that at all. Anyway, all the problems are solved - to test it I just connected everything with a small bolt (a non-fusible link).

Obviously this isn't a safe long term solution. I just have to figure out a way to wire that 80 amp fuse back in and get it to stay in place without the plastic housing.

Thanks to everyone for your help. In retrospect i feel like i should have figured this out sooner, but to be honest, the cover on the fuse box really threw me off - it labels the fuses in that spot as GLOW-AM and DIESEL. What's that about? It's not intuitive at all that that would be the main spot where power gets from your battery to so many of the systems in the truck.

 

That's AM1 or AM2 that melted, these are primary and secondary circuit protection, a quick guess would be due to high resistance and high current (resistance+current=heat)

Not digging out the book but from memory AM1 is between the battery, the alternator, and the rest of the system. Or the alternator output is between AM1&AM2..
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That plastic housing is part of the fuse, unless you mean the distribution box, I reckon yotayard or lots of users have an intact AM that's going to cost more in shipping than the part. If you've got a local salvage yard just about every yota from the era has the same fuses in it.

AM# is the important bit of that in addition to the ##A, basically you have AM1 in one of three places in the dist block based on the vehicle (LEAN manufacturing at its finest, they print one label for one style box, then use it in a dozen vehicle engine combos).

"It's not intuitive at all that that would be the main spot where power gets from your battery to so many of the systems in the truck."

They are all like this, it's not a Toyota thing, you have FL (safe fail) wire off the battery to a distribution block under the hood. Some call it a fuse box some call it a distribution block ect, but it's all the same. Just think of a tree roots as the battery and each branch/trunk is a fuse. Some are big some are smaller..

Glad you found it I don't recall if the FL repair kit is still available or the primary fuses, I'd expect so. RAD has some detailed threads about this junction.