96' Headlights Randomly Coming On While Vehicle is Off and Locked (1 Viewer)

[jht3]

I just tested this on my 97 LX450.
Door closed, ignition on. Switch headlights on.
Switch ignition off-lights stay on until door opens.
Once in this state, you must switch headlights off, and THEN the stalk switch controls headlights normally, regardless of door open/closed.

that's how i believe it is supposed to work. you should be able to turn the parking lights (and headlights) ON without the key in the ignition. in the case of the light timer relay, you must cycle the headlight switch OFF first.

my truck continues to misbehave today. as soon as i turn the truck/ignition off, the headlights and dash lights turn off. no way to turn the parking/head lights back on without cycling the ignition back on. i CAN flash the high beams, which is not part of the light auto turn off circuit, so that makes sense.

i don't suspect the headlight switch, as it works 100% WITH the ignition on. according to the EWD, the path to ground through the headlight switch (pin 11) is the same regardless of ignition on or off.

i do suspect that light retainer relay. i can't prove it, but it must have an internal failure, either not holding the relay open at ignition off or re-latching at random times. the ground path(s) are through pins 2 and 3, and therefore pin 11 of the light control switch.

or somehow the security system (TVSS in my '95) is messing w/ things. but i can't determine if it ties into the light circuit since there are no published schematics.

i'm going to try and source a used light retainer relay as the new ones are a bit much. in meantime when i get a moment (which is rare as work and kids consume every waking moment), i'll disconnect the relay and jump pins 7->3 and 8->2. that should allow me to cycle the lights on/off with the ignition off.

thanks for staying w/ me!

 

[jht3]

found some time to dig into the footwell. what a pain! but got the retainer relay out and pins jumpered. also tested the diode and it checked out (open in one direction, ~870 in the other)

headlights now work with the ignition off AND on. but obviously don't have the auto off function, but it wasn't working right anyways. that scotch lock seems "factory" and is tapped into the tail light relay (pin 8), and i *think* might be part of the port installed TVSS security/keyless system?

 

[jht3]

Well crap. Sourced a light retainer relay and absolutely no change in behavior. With the door closed, the lights immediately shut off with the ignition.

So I guess it is either the headlight switch, which otherwise is working fine, or something undocumented like the TVSS alarm system.

I don't have any key fobs, so I guess I will remove the old alarm as my next job.

 

[3ontwo]

Did you have any luck with this
Im having similar issues

 

[jht3]

Did you have any luck with this
Im having similar issues

me? no, not yet. the weather turned since i did my troubleshooting and i haven't felt like tearing into it. this truck has been my daily the entire time too. i left the jumpers installed for a couple weeks so the lights operated purely manually. i have since removed the jumpers and plugged the light retainer relay back in. the auto function has yet to start working again, and i can't control the lights at all with the ignition off. i try and remember to turn the lights off manually, but have forgotten once or twice with no gremlins turning the lights back on.

i'm going to start with removing the TVSS alarm. my hunch is that it is somehow grounding the relay or interrupting the headlight switch in some other way. i don't have any keyfobs anyways, so it is useless to me.

if THAT doesn't work, then that only seems to leave the headlight switch. but it is working in every other way, and my diagnostics of it show that it is within spec.

 

[3ontwo]

I removed alarm and installed a new headlight switch
No change lights still on
Any suggestions?

 

[jht3]

I removed alarm and installed a new headlight switch
No change lights still on
Any suggestions?

Have you tested the retainer relay? Or bypassed it?

 

[jht3]

UPDATE: it is now working. TLDR it was a loose connector on the ECU-B fuse.

deleted the TVSS the other day but auto off lights still completely dead. since the dash is still apart and seat out, now's the time to figure this out.

i found the light retainer relay test procedure in the FSM on page BE-15 (body electrical section). so i thought i'd test my spare relay, but nearly immediately let the smoke out. whoops.

so headed back out to the truck and probed the body harness side following the service hints section on page 89 of the EWD.

continuity between pin 5 and ground is supposed to exist with the drivers door open, and it does, but only for a split second; not constant as i was expecting. the door open buzzer goes off constantly however if the key is in the ignition. and the interior light stays on. puzzling.

but lo and behold, i wasn't getting +12V on the hot at all times black-red wire at pin 6. the hell? that's a bigger issue.

went upstream and tested for voltage at the ECU-B fuse; both sides. nothing. the hell? pulled the fuse and it was fine. even ohm'd it out...fine. stuck my probe in the now empty slots; +12V on one side, nothing on the other. ok, so i DO have voltage at the fuse box, but with the fuse in i get nothing. carefully inspecting the female pins one side looked opened up more than the other side. for all you married guys, it was like a hotdog down a hallway. pushed the pins together as best i could with a pick, shoved the fuse back home, and now voltage. as tight as a prom night.

tested the headlights and all is working again. no wonder this was intermittent.

looking at the EWD closer, and ECU-B feeds the ABS ECU, Airbag Sensor Assembly, SRS light in the dash, cruise control ecu, and data link connector 1. haven't noticed anything wrong w/ those so this is a head scratcher.