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First off, let me express my deep gratitude to everybody involved with this forum. I have found so much useful information over the years and spent many an evening pouring through somebodies build-up thread. I've gotten tons of help over the years just with searches, but this time I'm stumped. I need your help!
I've got a 91 4Runner 3.0 as my DD. Recently did a bunch of work on it, including taking apart the dash to replace the clutch/brake pedal bracket which had cracked. I also welded the floor up as it was badly rusted (mostly missing), but I did unplug the computer while welding. Also had gauge cluster out to replace speedo cable.
After buttoning everything up, a bunch of stuff wasn't working: front and rear heater blowers not working, no gauges working (except speedo, obviously), DRL does not turn on, no check engine light when key is turned on (or at all). No fuses are burnt out (although there is no power to the "engine" fuse) and the engine will start and run fine. The battery light illuminates when I turn the key on and goes out once the engine starts. The battery is charging normally while the engine is running.
Eventually I tried unplugging the 3 wire plug that goes into the back of the alternator, and poof everything works. Drove it like that for a few days, but last night just as I got home heater, gauges, etc. stopped working again. This time unplugging the alternator didn't help.
Among other things, I also tried unplugging the reverse sensor while troubleshooting, but this made no difference.
What I am looking for is any ideas about what else is on that circuit? I am disinclined to suspect a short since no fuses are burnt. Rather I am thinking that there is a switch or relay that is common to all of these things which is either sticking, corroded, or itself has a bad ground.
The wiring harness was mauled by a ham-fisted PO who was supposedly an electrician for CN Rail, but used the "strip, twist together, and electrical tape" method for installing aftermarket command start and cruise control... so anything is possible.
Sorry, this is a head-scratcher. The Engine fuse powers the alternator (and the cruise control, but not much else). So with no power to (from) the Engine fuse, the alternator should produce no output. More importantly, once you disconnect the 3-terminal plug from the alternator, it will definitely produce no output. I suppose you could run on just battery for a while as long as you didn't use the starter, blowers, or headlights much, but I would expect you'd run out of charge pretty quickly.
So you probably have a very "unique" wiring plan, thanks to CN Rail.
Trying to find some sort of common thread, I would recommend you check the output of the ignition switch. In my '93 EWD, IG2 (B-R) from the ignition switch powers the EFI relay and so on, but IG1 (B-Y) powers the Engine, Gauge, Wiper, and Turn fuses. http://web.archive.org/web/201204170.../2powersou.pdf Perhaps you've lost IG1 but not IG2. You'll need, obviously, your trusty multimeter.
Thanks Scope! That file was exactly the kind of information I'm looking for!
Unfortunately, it's left me more confused than ever... Ig1 should give power to gauge, wiper, turn, ecm-ig, and engine fuses. My wipers, turn signals, ECM, and alternator all work fine, but I've got no gauges or blower.
As far as I can tell, the "engine" fuse sends field power to the alternator and the "gauge" fuse sends power to the gauges and fan blower (and back-up lights?).
Checking fuses with my test light, all fuses check fine, with power on both sides, except "engine".
So basically, engine fuse isn't getting power, but the alternator is still getting power, and the gauge fuse is getting power but the gauges and fan blower are not.
Added to all this is that it is currently -34C (-30F) outside and I'm trying to troubleshoot this in my driveway. We'll actually I'm spending as much time as possible inside looking out the window at my driveway; "troubleshooting" on my computer looking at wiring diagrams, lol.
I'm thinking that I can rule out the ignition switch as power is being sent to the other fuses okay. I'm suspecting something in the junction box that holds the fuses, or potentially in the wiring harness somewhere (perhaps while installing the command start something on this circuit would have been tampered with).
In the wiring diagrams I'm looking at, what does MFI stand for? When they say combination meter, are they referring to the gauge cluster?
Combination Meter is Toyota-speak for instrument panel. Or gauge cluster. MFI and EFI are (more or less) synonymous.
If the alternator is charging the battery with no voltage on the Engine fuse, well, you must have some re-wiring. More importantly, if unplugging the alternator magically makes the gauges work, then I'm almost certain you've got an intermittent connection somewhere that you're just bumping into. The only connection between the combination meter and the alternator is the "Alt" light, and that connection to the alternator is designed to swing from ground (light on) to ~+14.1v (light off). So it's not like that wire is shorting to ground or battery and taking out the gauges.
You're just going to have get out the multimeter, take the dash back apart, and find out what got disconnected/broken. You might want to wait til it heats up to about -18°C; then you can work in shorts, eh?
Not having the cover for the fuses in the drivers side kick panel, I had gotten a picture of the fuse layout off Google.
While looking at it on my phone, I managed to get it sideways so the fuse I thought was "Engine" was actually "Tail" which explained why I had no dash illumination.
I made myself a fuse layout card:
When checking the fuses I had only probed with a test light to confirm they weren't burnt out; I pulled the fuse to check for power at the connection and bingo! Fuse socket was crusty but had power.
I next checked the gauge fuse and it was showing some powdery corrosion of some kind as well. I pulled all of the fuses and did my best to clean all the sockets, then replaced with new fuses. The gauge fuse was loose enough to only work intermittently when I wiggled it, so I bent the sides of the socket in slightly to make them tighter.
This fixed all the electrical issues I had been having.
Thanks again for your help Scope!
Btw, weather warmed up to a balmy -22C by the end of the day, so it wasn't too bad!
01-26-2021, 10:38 AM
so anything is possible.
