No head/tail lights or turn signals, squirrel chewed ground at J4

Howdy.
So after a heavy rain, everything controlled by the headlight switch is out.
The DIM relay buzzes loudly. I put in a new one, it buzzes but not as loudly.

I'm getting normal 12.47V at the HEAD relay, but only 11.4V at the DIM relay and 10.2V at the IG1 no.2 fuse inside the cab.
From what I've been reading, it could be a bad headlight switch on the steering column, a bad body ECU, or a bad red connection between HEAD and DIM relays.

Any way to pin it down? I don't want to guess, pretty sure I can change the switch myself, not sure about the other 2.

Thanks in advance.

Edit: There are no ODB error codes showing.
#2: Also, not a speck of voltage at the 10A headlight fuses that the W and R-B wires go to.

 

The IG1 No 2 Fuse is powered by the IG1 Terminal (Pin 1 (Blue/Yellow)) of the Ignition Switch, See if you have the same voltage drop at the IG1 Fuse (10A) and ACC Fuse (7.5A). If you have the same voltage on those as on the IG1 No 2 then you likely have an issue with the AM1 circuit or the feed to the AM1 Fuse (50A), if you have the voltage drop on the IG1 Fuse but not on the ACC Fuse you more likely have an ignition switch issue.

 

Thanks!
ACC = 12.37V
IG1 = 12.32V
IG1 no.2 = 10.42V

Is testing the ignition switch an option?
I don't quite get how IG1 and IG1no2 can be showing different voltage when they're powered by the same wire? If I'm reading the diagram right...

 

That is interesting, have you pulled to fuse to see if there's any corrosion?

 

Yep, all three of those fuses look great. I did have to pull them to test, couldn't seem to get a reading from the tabs on top.
Seems like everything else related to the low voltage IG no2, which is lots, is perfectly fine?

 

What about the WIP, WSH, and 4WD fuses, do they have the same voltages?

 

Just checked them- wipers and washer correct, 4WD fuse is only 9.5V?
Thanks again, back in 20 minutes gotta hit the store.

 

So it would seem something is going on in the driver's junction box/fuse box/body ECU.

You said it was after a heavy rain, I wonder if it got water in it.
Did you notice any water leaks in the cab?

 

I felt around, didn't seem to be any moisture inside the cab at all.
Is it easy to pop that fuse box apart? Anything other than fuse holders that can be tested there?

 

I'm not sure, I haven't had one apart.
If your checking the right fuses then it really can't be anything else other than an internal issue in the box.

The Body ECU lives on the back of it and that controls the HEAD and DIM relays which you sad the DIM relay was buzzing.

 

Would there be any ground connections that should be checked?
Is the upside down L-shaped gray area on pg.2 of the diagrams you posted the ECU?
Also, is that dead-end Y-B wire coming from the DIM relay a ground? Same for the dead-end W wire coming from HEAD relay?

 

The grey area is the fuse box.
The Y-B wire is a ground.
The ECM controls the ground on that wire.

 

You could check 1H Pin 18 (White/Black) and 1L Pin 7 (White/Black).

Toyota refers to it as the Driver's Side Junction Box, it shows up as a single unit on the wiring diagrams but it contains a junction box, fuse box, and the Body ECU all in one box.

Those are the control wires for the relays, they are ground side switched. The Body ECU grounds those wires to turn the relays on.

 

The Ground in question for the Body ECU is at Ground Point IA behind the Left Kick Panel.

 

So would the Y-B wire being loose cause the DIM slots to test at semi-normal voltage, but then short out when the relay is plugged in?
Which of the 5 pins on the DIM relay is ground, the center one?
If I recall correctly, the DIM slots tested 11.4ish volts with the black probe in the center and red on different outer slots for high and low beam, not positive it might have been outside to outside slots.

 

I'd use a test light connected to battery Positive to check the control pin of the relay.

Pinout of the relays below, Pin 2 of the DIM Relay is the control pin and Pin 1 of the HEAD Relay is the control pin.

 

Would a bad/fried Y-B wire cause the buzz when the ECU tries to turn the relay on?
The buzz is a lot louder when on high beams than low. Seems like a bad Y-B would cause silence, but I'm no expert.
One other odd thing is the smaller A/F Heater relay right next to the DIM seems to get warmer than it should, not sure what that one does.

 

Have you checked powers and grounds at the relay terminals?
Use a test light if you can.

 

Check pins 1 and 3 for power on DIM relay.
And 2 for ground with the head lights turned on.

 

I mean a poor connection/corrosion could cause that I suppose but being a relay only needs about 150 mA to close I wouldn't think it's a fault in that wire. In any case that wouldn't explain the power loss at the IG1 No 2 and 4WD Fuses.

Now if the Body ECU itself had a poor ground it would be unable to properly ground those relays and could cause them to buzz.

It's normal for a relay to get warm when it is energized for an extended period.