Hi beams randomly turn on

So right after I just swapped out my transfer case actuator, my high beams are randomly turning on when my low beams are on. All of a sudden, they switch on, and you can't turn them off with the toggle. It has no effect. Only by flipping to running lights a s back to low beams do the high beams turn off. Sometimes the process repeats, sometimes they stay off. Can anyone offer any advice?

 

Just had this happen last night, did you find a solution? I’m hoping it’s a relay or something simple, tracing electrical gremlins makes my head spin.

 

the high beam really your be my first point to check then the wiring for damage on the control side of the relays (assuming stock assemblies)

 

The High and Low beams selection is controlled by the Body ECU on the back side of the fuse panel to the left of the steering wheel behind the change drawer. It turns the Dim Relay (Under Hood Fuse Panel) On/Off. Check the relay and the connections on the Body ECU for a loose connection.

DIM Relay location under hood fuse panel.



Body ECU with cover removed.

 

You Guys rock, thank you...I'm heading out now to try to diagnose.

 

OK, so after all kinds of digging it turns out the issues with the hi-beams were a sign of corrosion with one of the main engine harness junction boxes. Corrosion seems to be as a result of exposure to moisture but not due to the usual suspects…evap drain line, leaking windshield, etc.
My local independent (and remarkably capable) auto shop reached out to Toyota for parts to repair the specific corroded pins but apparently Toyota would only sell the entire harness assembly. Repairs (splices, unfortunately) are currently underway, more details to follow shortly.

 

You can absolutely buy the terminal independent of the whole harness.

 

Any chance you could share a part # or link?

 

If you know which connector it is in the fuse box, sure. Once I (you) know what connector it is, you’ll know the part number. Once you know the part number. Use the link below to find the connector and then find the terminal.
https://www.toyota-tech.eu/wire_harness_rm/RM06H0E.pdf

 

Pics of this identified connector?

 

In the next day or so, still at the shop

 

Sounds like it’s the IA1 Junction Block?

 

IA1 isn't a junction block, it's a pass-thru connector that joins part of the interior harness to part of the engine bay harness.