Right turn signal comes on with brake lights

It only does it when it is fairly cold out and when it sits overnight. I will get into my 2000 4.0 Explorer and when I put my foot on the brake my right side turn signal comes on, it doesn't flash it just comes on and stays on. When I let off the brake it goes out. It will do it maybe four or five times and then work fine all day. Its just the right side and the indicator on the dash comes on too. Any body have any ideas? I haven't looked at a wiring diagram yet to see if there is a connection between the two.

Issues like this are typically indicative of a grounding issue. If a ground for the rear brake lights goes high in resistance it looks for another path to ground. Sometimes this is through a filament of a bulb to ground. In your case, it sounds like it's energizing the right turn signal circuit and likely grounding through the front right turn signal bulb.

I'm going to guess that somewhere along the way someone installed an aftermarket trailer light plug and tapped in to the existing wires rather than using the correct pigtail connector. They next failed to properly seal the connections and not the connections are corroding, causing your grounding issue.

-Rod

The trailer plug is plugged directly into the factory connector. I haven't seen any tapped wires. I thought with a ground issue it would do it more consistently? It only does it when it is fairly cold out and sits overnight and only does it maybe 5 times and is fine the rest of the day.

Yeah, good point. A ground issue would likely be more consistent, such as when it's humid, or all the time.

The brake lights will route through the Multifunction Switch (MFS) which also handles the turn signals and hazard lights. I have read of a lot of issues with connections near the MFS in the steering column, but again those issues would likely be more consistent, unless you adjust your steering column tilt to get out of your Explorer at night, then adjust it back down in the morning....

-Rod

When the issue is happening, if you turn on the right turn signal, do the turn signals work properly? How do they behave if you use the Hazard lights?

-Rod

My steering wheel doesn't get moved, but I do believe I have multifunction switch issues. Now and then when I turn on my turn signal, my wiper will swipe once. That one is real intermittent and once in a great while when the wipers are on delay the timing changes for a split second and goes back to where I have them set. I don't remember if the turn signals work when it happens or not and I never tried the hazards. Next time it does it I will have to see...

It finally done it again. I was messing around with it and when it does it the right turn signal does not work until I let off the brake pedal. After holding my foot on the brake and having the right turn signal on for a few seconds, the switch stated smoking. So i have come to the conclusion that I need to replace the switch, which I just did today.

Issues generally are easier to find once you let the magic smoke out, at least if you are present to see the magic smoke.

Hopefully this solves your issues!

-Rod