Headlights only work when truck running, and switch off

Hi folks, newbie poster here.
Just bought a 2002 Tacoma ext cab 4x4 3.4 and several weird issues I believe are all related. looking for advice as I can't find anything similar online.

Original owner, no mods but left parked for a month, that's when issues occurred.

1st issue, headlights only work when truck is running and switch is off. Pulled switch and disconnected from plug at switch. Lights then stay on when running.
I can hear and feel the headlight relay when I use the switch, but no effect on the headlights. The running and tail lights work as they should from the switch. Using highbeams also turns the lights off when truck is running, and has no effect when headlight switch is on, but I can also hear the relay click when I engage the highbeams.
It had an alarm and lock remote, which I removed but no effect.
Not sure how headlights are getting power, if not from the relay circuit, seemingly from the alternator.

Also, and the owner stated it happened at the same time as the headlights (from being parked); the tach and the temp gauge don't operate. My research says ECM potential failure on this. I checked fuses, but all seem good. I also don't see any indication light on the dash when I engage the 4x4

Does the headlight circuit also go through the ECM? Could this all be from a malfunctioning ECM?

Thanks in advance for any help. I can't seem to find the right wiring diagram for my specific rig.

 

Maybe rodent damage since it sat there for a while. Inspect the wiring the truck. Something maybe shorting out and causing these weird electrical issues

 

Yea, I have looked and dismantled the dash etc. I haven't pulled the instrument panel yet, but no obvious wire damage. I also pulled the fuse block under the hood up and have been wiggling wires while the switch is on and the truck is off to see if indeed a short is the cause, but no luck

 

I'd at least try swapping the relay with another one just to see what (if anything) happens differently

I'd also be suspicious of under hood rodent damage to some part of the harness.

 

see if you can get another headlight/turn signal switch on there and see if that does anything. Maybe a bad switch

 

Thanks folks. Bill; I tried to find another relay under the hood that matched the headlight one, but the configurations were different.
213; When I removed the switch (and disconnected) the headlights stayed on (not the running lights). I would have expected that with no switch, there would be no way for power to get to headlights.
Does anyone know where to get a wiring diagram? Also, does anyone know if the headlights are controlled by the ECM in any way?

 

my bad I read wrong. Try the relay as mentioned above

 

read this

Headlights won't turn off, even with ignition off | Tacoma World

 

Thanks 213. I will probably try the relay first.