Stray Voltage Parking Light Circuit

[Gulah]

I just installed a new plug-and-play trailer wiring harness (hopkins 43415) and while testing noticed a constant 1.2V/1.3V (vehicle off/running) between ground and the brown trailer wire (tail/marker lights). Previously I had noticed a slight glow of my front LED parking lights when the vehicle was running, though I can't duplicate at the moment.

Has anyone else experienced this and hunted down the root cause? My battery was once dead after sitting ~1 month and I'm inclined to think this is the reason.

Thanks

 

[gamefreakgc]

I just installed a new plug-and-play trailer wiring harness (hopkins 43415) and while testing noticed a constant 1.2V/1.3V (vehicle off/running) between ground and the brown trailer wire (tail/marker lights). Previously I had noticed a slight glow of my front LED parking lights when the vehicle was running, though I can't duplicate at the moment.

Has anyone else experienced this and hunted down the root cause? My battery was once dead after sitting ~1 month and I'm inclined to think this is the reason.

Thanks

Note: I have the towing package in my 4Runner.

Make sure it's a true plug and play wiring harness. It needs to decipher a 5-wire signal and condense it to 4 for the trailer. At my local auto parts stores I had to do a manual wiring job and it came out just fine. It might have jumbled up the wiring in ways that it's not supposed to.

I THINK that one works, but it was out of stock when I was looking and didn't use it, I used the universal one. I would double check you have the right wires hooked up.

EDIT: Also check that the ground is good, bad grounds cause funny issues. This is the one I used: https://www.amazon.com/dp/B0002Q8036/ref=psdc_15737351_t5_B0002Q7ZLO but bought from NAPA.

 

[Gulah]

Note: I have the towing package in my 4Runner.

Make sure it's a true plug and play wiring harness. It needs to decipher a 5-wire signal and condense it to 4 for the trailer. At my local auto parts stores I had to do a manual wiring job and it came out just fine. It might have jumbled up the wiring in ways that it's not supposed to.

I THINK that one works, but it was out of stock when I was looking and didn't use it, I used the universal one. I would double check you have the right wires hooked up.

EDIT: Also check that the ground is good, bad grounds cause funny issues. This is the one I used: https://www.amazon.com/dp/B0002Q8036/ref=psdc_15737351_t5_B0002Q7ZLO but bought from NAPA.

Thanks for the reply. Yes, it is definitely a true plug-and-play harness with converter designed for toyotas and recommended a few times on this forum. It seems to be functioning fine, showing 12V at each pin at appropriate times.

Regardless, I don't know how there would be a 12V or 1.2V source in the taillight area with key/lights off.

 

[phattyduck]

Have you converted all your exterior bulbs (at least on the parking light circuit) to LED? That voltage would be consistent with the voltage across an LED drawing a very small amount of current.

-Charlie

 

[Gulah]

Have you converted all your exterior bulbs (at least on the parking light circuit) to LED? That voltage would be consistent with the voltage across an LED drawing a very small amount of current.

-Charlie

Yes, my front parking lights and tails are LED.

I'm worried my OP wasn't clear, sorry. I am seeing 1.2-1.3V between the parking light circuit (brown trailer wire) and ground with all lights switched off and the vehicle off. If the vehicle is running the voltage slightly increases due to the alternator. When the parking lights are turned on I see ~12V as I should.

There's leakage somewhere from constant 12V -> parking light circuit.

Thanks for the reply.

 

[gamefreakgc]

I re-read your first post and might have misunderstood. Are you saying you had the draw before you installed the brake light converter box?

 

[Gulah]

I re-read your first post and might have misunderstood. Are you saying you had the draw before you installed the brake light converter box?

I once noticed a light glow from the front LED parking lights while the vehicle was running with the lights switched off, prior to the installation of this trailer harness. I can't duplicate that presently, but my battery isnt fully charged. This leads to believe that yes, this issue existed prior to the harness. Also, all of the feeds to the harness should have 0V with the lights/vehicle off since the switching is done upstream. Unless I'm missing something?

The amount of leakage could also be variable if there's a fraying wire somewhere.

 

[Gulah]

Update:
I pulled fuses and relays from the engine bay fuse box and found that when pulled the dome fuse the voltage between brown trailer wire (tail/marker lights) and ground immediately dropped to 250mV from 1.25V, and then slow drifted towards 0V over a period of many minutes.

Anyone have any guesses where these circuits could be interacting? I bought the vehicle recently, and the only aftermarket wiring im aware of is an older sony stereo and an old spliced trailer harness that I removed and insulated. Thanks

 

[phattyduck]

The Tail and Dome fuse outputs meet in a few places (like the clock). I can imagine a small amount of bleed between those circuits.

Can you put back one regular bulb in the parking light circuit and see if it still does it?

LEDs don't start drawing current until around 1.2V (for red/amber), which matches up with what you are seeing. Bulbs have very low resistance until the filament heats up, which would keep any small amounts of stray current down at a very low voltage - the LEDs won't do that.

-Charlie

 

[19963.4lsr5]

I solder 22k ohm resistors across the LEDs to keep them from glowing.


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[Gulah]

I think you nailed it! Voltage goes away with the clock removed. Sorry for the slow reply, I regrettably missed the notification for this.

I would have never guessed it, but sure enough the FSM confirms. Thanks for all the help everyone!

The Tail and Dome fuse outputs meet in a few places (like the clock). I can imagine a small amount of bleed between those circuits.

Can you put back one regular bulb in the parking light circuit and see if it still does it?

LEDs don't start drawing current until around 1.2V (for red/amber), which matches up with what you are seeing. Bulbs have very low resistance until the filament heats up, which would keep any small amounts of stray current down at a very low voltage - the LEDs won't do that.

-Charlie