2004 Double Cab - Parking Lights do not turn off

1- turn headlights on and off, the parking lights (front and rear) and license plate lights stay on. Turn off ignition and they remain on
2 - pulled 15a fuse on inside fuse panel and lights go out, with ignition off
3 - put fuse back in and the lights turn on, with ignition off
4 - i can hear the relay click on and off for the head lights.
5 - i suspect there is a relay for the parking lights on the back side of the fuse panel
6 - how do I access them, and which one is the parking light relay?
7 - only way to turn them off is to disconnect the battery.

 

Dealer-installed, or aftermarket alarm at play?

Is the windshield currently cracked?

Has the windshield ever been replaced?

 

I am the original owner, there have been no after market or dealer installed alarms or remote start etc.
Windshield is good, truck has been parked under a carport for the past several years. I looked for water damage around the fuse box but could not see any.
maybe i need to look closer, but nothing obvious
Windshield has been replaced a few times.

 

Had to ask, based on prior cases, hope you understand.

Water intrusion into the fuse box does happen pretty commonly on these trucks but it sounds an awful lot like a stuck relay to me. Especially that it magically “clears” with power disco. That would be the one thing that would likely make a stuck relay unstuck.

@BubbaW is the king of electrical, in my book. I reckon he’ll have some good ideas.

 

Could be the switch too.

 

Are the dash/panel lights on all the time as well?
They are on the same circuit as the parking lights.
The TAIL fuse powers both.

Is it possible the TAIL relay is stuck in the on position?



And yes, the taillight relay is in the under-dash fuse box.

 

of course I am trying to test whether the dash light stays on with the sun out, but yes, dash light stays on when lights are turned off.
i can see the relays on the back of the fuse panel, but i can't get my hand in there, do i have to remove the panel to access them?

 

But you do have "Anti-Theft system with remote keyless entry", which was a Standard feature for 04 DC LTD ? Those 2 can play a part but are the least likely.

Definitely concur with the below, including the question below in bold @1lowlife asked.

There's not an easy place to start given taillight relay location, light control switch(combination switch) and the Body ECU(up above cab fuse panel) which is part of the circuit that gives ground signal to taillight relay, as shown in the Taillight circuit @1lowlife posted.

edit: noticed the below after preparing to post....

Yes, you'll have to remove lower finish panel and then attempt to get to taillight relay. I would definitely unhook battery when doing some of these checks. In case you have ot trouble shoot combination switch, the below video should help.

May be more than you need but I'll post it just in case....

 

I swapped the TAILLIGHT relay with the FOG Light relay, which did not solve the problem.
going to pull the light control switch (combination switch) now and test it as you specify above.

 

light control switch tests ok for continuity.

i think that leaves the Body ECU. Any guidance on what to look for or how to test it?

 

Just to make sure….you checked the switch itself with connector unplugged with switch in OFF position….pin 14 & 16 ?

As for the body ecu, will have to check when I return home later this evening, sorry. That’s a bugger to get to.

Can you also answer from a previous post, you do or don’t have "Anti-Theft system with remote keyless entry" ?

 

yes, i removed the light control switch, and used a multimeter, and switched back and forth between off and tail, there was continuity between 14 and 16 when switched to TAIL, and then switched to HEAD and tested 16 to 13 and 16 to 14 which had continuity. no continuity when switched to off.

 

Something is grounding your light circuit.
I'm no mechanic but I don't think the ECU is the problem.

Do you have a trailer light plug on your truck?
Have you checked the wiring looms under the truck, bed and spare tire?

There have been threads about crushed wire looms shorting and/or grounding circuits.

 

This too was on my mind.

Too many ignorant folks think these things are OK to use. On exterior wiring, it's not a matter of "IF" but "WHEN" your wiring is fucked. These Quicktaps/Scotchloks and related T-taps really butcher your wire casings, and sever strands of wiring, then oxygen takes its toll to corrode the wires and ... you're screwed. Sadly, some of these were used on the earlier models to dealer-port tow wiring on.

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Does the dome light come on when you open the door?