EDIT SOLVED: Problem was Auto-Off feature located behind instrument cluster. Jumped pin 5 to pin 1 on c27 harness to bypass auto off feature.

Recently bought #4 and slowly going through the vehicle getting rid of rust and making things right.

1999 4runner Limited w/o DRL and w/fogs

My headlights stopped working recently when operated from the stalk switch. The parking lights will come on but the headlights will not. The high beams will come on when i pull the lever to "flash" them but not when i push the lever forward for normal high beam operation.

I know the bulbs are good because I've been jumping the HEAD relay in order to drive at night and also i can "flash" the high beams on.

I have checked/tested/replaced all relays and fuses. I have a complete parts truck (#3) i can steal parts from. It has a different Body ECU though...

I have a complete extra headlight stalk/switch i have tried so its not the switch.

HERE IS MY PROBLEM: On the coil side of my HEAD relay i have 12v and 0v with lights off. When i turn the lights on from the headlight stalk switch, i have 12v and 8v at the coil!!

So somehow, 8v is back feeding to the coil on the HEAD relay. From what i understand, instead of getting the additional 8v I should be getting continuity to ground once the lights are switched on. Ive checked both continuity to ground and voltage (8v) and i seem to have both on that side of the coil.

So i started tracing that 8v back to the Body ECU (red wire). I then started unplugging harnesses (there's 12...) until i lost the 8v. The harness that i unplugged which made the 8v go away had two incoming 12v wires. Black w/orange (goes to defog relay under hood) and Blue w/yellow (goes to DOME fuse under hood). I unplugged the defog relay, still had 8v. I unplugged DOME fuse and Boom, 8v goes away. But... without the DOME fuse, there is a lot of stuff that doesn't work!

WHERE IM AT NOW: The DOME circuit feeds 12v into the Body ECU and somehow 8v leeches through to the red wire which leaves the Body ECU and goes to the coil of my HEAD relay.

Does anyone know how the AUTO-OFF FEATURE works or have a diagram of the DOME circuit?! Once the ignition is off and the driver door is open it will automatically shut off the headlights. This will also trigger the DOME lights to come on so i assume they work together.

I traced the wires around the best i could and even took apart the Body ECU and cleaned up a little corrosion inside. My best guess is that the circuit board in the Body ECU has some components that got fried somehow. Im going to the junkyard tomorrow to hopefully find a new Body ECU to test. Considering im getting a consistent 8v leeching i would assume the problem is a resistor or relay and not a compromised wire somewhere in the vehicle.

Any suggestions or insight would be amazing, i know there are a few guys on here who have a lot of in depth experience with these trucks. Hope you guys see this!

@TheDurk
@OrangeTexan
@phattyduck

EDIT: It looks like the Body ECU/ Junction Box is reasonably priced so i will try to find one in the junkyard tomorrow or buy one online.

This jumped out at me... There should be absolutely zero corrosion inside the body ECU. Was the corrosion next to the electrolytic capacitors (little vinyl sleeved can looking things)? If so, your body ECU needs to be repaired (caps replaced) or replaced.

-Charlie

Hey Charlie, thanks for the reply. So obviously corrosion in the Body ECU isn't a good thing and there was certainly plenty of it... ironically though, there was no signs of corrosion on the actual circuit board within the Body ECU, it was all throughout the "triple layered junction circuits". I don't know what to call it but its three layers sandwiched together. It doesn't contain relays or capacitors but only metal strips that route signals/voltage/current around... I cleaned all corrosion, soldered a couple new pins in place of some that had broken or corroded apart, and generously coated all the layers with dielectric grease before re-assembling the unit.

Regardless, today i went to the junkyard and got a new (used) Body ECU. Once plugged in, the truck experienced the exact same issues from before. So at this point im almost certain i have a grounding issue. Not sure where but somewhere. The headlight switch is supposed to be grounded somewhere...

Tomorrow im gonna trace from the Body ECU to the stalk/switch and see if i can provide a ground there. I read another thread with identical problems and the solution was something to do with the instrument panel. I couldn't make sense of that thread tonight but i will begin there again tomorrow.

Looking for some excellent wiring diagrams of the headlight switch to Body ECU tonight

That would make sense - the auto light turn-off is controlled in the gauge cluster, not the body ecu.

-Charlie

I bypassed the Auto-Off and the lights began working.

I got a new gauge cluster circuit board today and everything is back to normal working order. Only difference now is my truck gained 40k miles on the odo... facepalm.

Have you heard of anyone being able to repair this circuit board? It would be nice to maintain my current milage.

As a side note, i chose a circuitboard from a 2wd gauge cluster just to see if it would work. It did. The circuitboards seem to be interchangeable for 2wd and 4wd from 99-00 and possibly all the way through 02. The guage cluster on the 2wd didn't have the 4wd indicator light cutout between the blinker indicators but the circuitboard still worked on my gauge cluster.

Thanks for all your help, im so glad i didn't have to chase ghost voltage around looking for a bad ground!! haha

2WD complete gauge cluster works on a SR5 4WD for 99/00 4Runners. They have the 4WD light over by the gas gauge (and even a spot for the rear diff lock light). The multi-mode 4WD indication is used on the 99-00 4WD Limiteds and all 01/02 4WD 4Runners. The 01/02 cluster is likely different due to having traction control.

It is possible to reprogram the cluster mileage if you have soldering skills and an EEPROM programmer...

-Charlie

I do have soldering skills. I was looking at the boards wondering where the milage was stored. Would you happen to know where the EEPROM chip is on the board? Ive narrowed it down to two chips, one is the IC6 chip (93C56) and the other is the IC3 chip (93C46). Im sure they both store something but which is the odometer reading... and what the heck does the other do?! LOL. Surely it can't be immobilizer data...

EDIT: Maybe one stores mileage data and the other stores speedometer calibration data?

I don't know the specifics, but have seen write-ups on it. It should be similar on other Toyotas of the same vintage. I can tell you that immobilizer data is on its own EEPROM in the ECU...

-Charlie

Thanks for all your help. Yeah ive read a lot on it and i havent found anywhere that mentions there being two ROMS on this particular board. Based on everything ive found so far it could be either one.

The thread about the immobilizer ROM was really cool, if i ever lose my key ill be attempting that before i buy a new ECU😂

The search continues!

Had the same issue. Thanks for posting the solution. Made a video about it.

https://www.youtube.com/watch?si=E7VSGzlJGxZSryy_&v=Iwbeo3iXDXw&feature=youtu.be